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PubMed2000

Designed evolution of enzymatic properties.

By providing a simple and reliable route to enzyme improvement, directed evolution has emerged as a key technology for enzyme engineering and biocatalysis. Recent advances include the evolution of a novel catalytic activity using the alpha/beta barrel scaffold, evolution of a cofactor-free monooxygenase, and the engineering of regulatable enzymes. New screening systems for enantioselectivity and protein solubility, and the continuing stream of new methods for creating enzyme libraries further extend evolution's reach.

Biotechnology↗

PubMed2000

New media technology and youth: trends in the evolution of new media.

An information environment is emerging from the simultaneous, rapid, and interconnected evolution of transmission systems, interfaces, and content quantity, quality, and structure. It will be easy to underestimate the collective impact of the sum of these changes on how young people communicate and absorb information. Ultimately, it will be more important to understand how these technologies will facilitate, amplify, or alter the cognitive processes and/or social behavior of the Internet generation. The article analyzes the impact of the following trends on media use and cognition among youthful users: * Information expansion and overload: Accessible networked information will continue to grow at a rapid pace for at least the next 10-20 years. * Rapid increase in interface diffusion: The number of access points into the Internet is expanding in number, variety, and mobility. * Evolution toward more embodied computing: Interfaces are evolving to use more of the sensorimotor system to transfer information to and from the user. * The evolution of more intelligent sensors to interpret use behavior and intentions. * Evolution toward anthropomorphic agent techniques: Computers are evolving to use more social and interpersonal communication techniques to interact with the user.

Adolescent↗

PubMed2002

Evolution of viviparity: what can Australian lizards tell us?

Historically, Australia has been important in the study of, and the development of hypotheses aimed at understanding, the evolution of viviparity in amniote vertebrates. Part of the importance of Australia in the field results from a rich fauna of skinks, including one of the broadest ranges of diversity of placental structures within one geographic region. During the last decade, we have focussed our studies on one lineage, the Eugongylus group of skinks of the subfamily Lygosominae because it contains oviparous species and some that exhibit complex placentae. Our specific objective has been to attempt to understand the fundamental steps required when viviparity, and ultimately complex placentae, evolve from oviparous ancestors. We have taken a three-prong approach: (1) detailed study of the morphology and ontogeny of the placentae of key species at the light microscope level; (2) study of changes in the uterus associated with pregnancy, or the plasma membrane transformation; and (3) measures of the net exchange of nutrients across the placenta or eggshell of key species. In turn, we have found that: (1) details of the morphology and ontogeny of placentae are more complex that originally envisaged, and that the early conclusions about a sequence in the evolution of complex placentae was naïve; (2) a plasma membrane transformation occurs in viviparous, but not oviparous lizards, and thus may be a fundamental feature of the evolution of viviparity in amniotes; and (3) species with more complex chorioallantoic placentae tend to transport more nutrients across the placenta during pregnancy than those with simpler chorioallantoic placentae but, because the correlation is not tight, the importance of the omphaloplacenta in transporting nutrients may have been overlooked. Also, the composition of yolk of highly matrotrophic species is broadly similar, but not identical, to the yolk of oviparous species. Some of the interpretation of our data within the context of our specific objective is not yet possible, pending the publication of a robust phylogeny of Eugongylus group skinks. Once such a phylogeny is available, we are in a position to propose specific hypotheses about the evolution of viviparity that can be tested using another lineage of amniotes, possibly Mabuya group skinks.

Animals↗

PubMed2002

The evolution and formation of RH genes.

The Rh system clinically is one of the important blood groups. The major Rh antigens, which are constituted by over 40 types, are RhD, RhC/c, and RhE/e. Furthermore, Rh blood group system is characterized by the existence of many variants. It was considered that Rh blood group system was encoded on two genes termed the RHCE and RHD, which are composed of ten exons, respectively. It is inferred that the RHD gene encodes the RhD antigen and that the RHCE gene encodes the Rh C/c and RhE/e antigens. There are RHce, RHCe, RHcE and RHCE alleles as polymorphisms of RHCE gene. In 2000, the entire nucleotide sequences in all introns of both the RHD and RHCE genes were determined. Due to the new findings on RH genes, it is thought that multiple recombination (and/or gene conversion), nucleotide substitutions, small nucleotide gaps, replication slippage of microsatellite, large nucleotide gaps (due to Alu sequence) and the high level of the homology (%) between both RH genes are the important factors in the formation and evolution of both RH genes and Rh variants. Based on the advance of human genome project, the new interpretations on the evolution and formation of RH genes and Rh variants will be performed. Human Rh family (superfamily) and its counterparts in primates, mammals, fish, amphibians, bacteria, lower eukaryotes, archaea and plants have been identified. A lot of findings have been accumulated in their evolution and function. As gene conversions or recombination events confuse the phylogenetic tree of human RH genes and their counterparts, careful attention is necessary for researchers to calculate the time of gene duplication and to discuss the evolution of Rh family and its counterparts.Rh genotyping methods will never be perfect and both the clinicians and researchers have to recognize the limitation of Rh genotyping, especially RhD genotyping, because new Rh variants must have formed continually. In applying the Rh genotyping to clinical medicine, especially transfusion medicine, it is necessary to compare and examine the serological (phenotypic) data in Rh blood group system with caution.

Journal Article↗

PubMed2004

Intratumoral patterns of clonal evolution in meningiomas as defined by multicolor interphase fluorescence in situ hybridization (FISH): is there a relationship between histopathologically benign and atypical/anaplastic lesions?

Meningiomas are cytogenetically heterogeneous tumors in which chromosome gains and losses frequently occur. Based on the intertumoral cytogenetic heterogeneity of meningiomas, hypothetical models of clonal evolution have been proposed in these tumors which have never been confirmed at the intratumoral cell level. The aim of this study was to establish the intratumoral patterns of clonal evolution associated with chromosomal instability in individual patients as a way to establish tumor progression pathways in meningiomas and their relationship with tumor histopathology and behavior. A total of 125 meningioma patients were analyzed at diagnosis. In all cases, multicolor interphase fluorescence in situ hybridization (iFISH) studies were performed on fresh tumor samples for the detection of quantitative abnormalities for 11 different chromosomes. In addition, overall tumor cell DNA content was measured in parallel by flow cytometry. iFISH studies were also performed in parallel on tissue sections in a subset of 30 patients. FISH studies showed that 56 (45%) of the 125 cases analyzed had a single tumor cell clone, all these cases corresponding to histologically benign grade I tumors. In the remaining cases (55%) more than one tumor cell clone was identified: two in 45 cases (36%), three in 19 (15%), and four or more clones in five cases (4%). Overall, flow cytometric analysis of cell DNA contents showed the presence of DNA aneuploidy in 44 of these cases (35%), 30% corresponding to DNA hyperdiploid and 5% to hypodiploid cases; from the DNA aneuploid cases, 35 (28%) showed two clones and 9 (7%) had three or more clones. A high degree of correlation (r >/= 0.89; P < 0.001) was found between FISH and flow cytometry as regards the overall quantitative DNA changes detected with both techniques, the former being more sensitive. Among the cases with chromosome abnormalities, the earliest tumor cell clone observed was frequently characterized by the loss of one or more chromosomes (64% of all meningiomas); loss of either a single chromosome 22 or, less frequently, of a sex chromosome (X or Y) and del (1p) was commonly found as the single initial cytogenetic aberration (30%, 5%, and 5% of the cases, respectively). Interestingly, an isolated loss of chromosome 22 was only found as the initial abnormality in one out of 14 atypical/anaplastic meningiomas, while the same cytogenetic pattern was present in the ancestral tumor cell clone of 32% of the benign tumors. Cytogenetic patterns based on chromosome gains were found in the ancestral tumor cell clone in 4% of the patients, 2% corresponding to tetraploid tumors. Overall, cytogenetic evolution of the earliest tumor cell clones was frequently associated with tetraploidization (31%). Our results show that meningiomas are genetically heterogeneous tumors that display different patterns of numerical chromosome changes, with the presence of more than one tumor cell clone detected in almost half of the cases including all atypical/anaplastic cases. Interestingly, the pathways of intratumoral clonal evolution observed in the benign tumors were different from those observed in atypical/anaplastic meningiomas, suggesting that the latter tumors might not always represent a more advanced stage of histologically benign meningiomas.

Adolescent↗

PubMed2001

The evolution of male mate choice in insects: a synthesis of ideas and evidence.

Mate choice by males has been recognized at least since Darwin's time, but its phylogenetic distribution and effect on the evolution of female phenotypes remain poorly known. Moreover, the relative importance of factors thought to underlie the evolution of male mate choice (especially parental investment and mate quality variance) is still unresolved. Here I synthesize the empirical evidence and theory pertaining to the evolution of male mate choice and sex role reversal in insects, and examine the potential for male mating preferences to generate sexual selection on female phenotypes. Although male mate choice has received relatively little empirical study, the available evidence suggests that it is widespread among insects (and other animals). In addition to 'precopulatory' male mate choice, some insects exhibit 'cryptic' male mate choice, varying the amount of resources allocated to mating on the basis of female mate quality. As predicted by theory, the most commonly observed male mating preferences are those that tend to maximize a male's expected fertilization success from each mating. Such preferences tend to favour female phenotypes associated with high fecundity or reduced sperm competition intensity. Among insect species there is wide variation in mechanisms used by males to assess female mate quality, some of which (e.g. probing, antennating or repeatedly mounting the female) may be difficult to distinguish from copulatory courtship. According to theory, selection for male choosiness is an increasing function of mate quality variance and those reproductive costs that reduce, with each mating, the number of subsequent matings that a male can perform ('mating investment') Conversely, choosiness is constrained by the costs of mate search and assessment, in combination with the accuracy of assessment of potential mates and of the distribution of mate qualities. Stronger selection for male choosiness may also be expected in systems where female fitness increases with each copulation than in systems where female fitness peaks at a small number of matings. This theoretical framework is consistent with most of the empirical evidence. Furthermore, a variety of observed male mating preferences have the potential to exert sexual selection on female phenotypes. However, because male insects typically choose females based on phenotypic indicators of fecundity such as body size, and these are usually amenable to direct visual or tactile assessment, male mate choice often tends to reinforce stronger vectors of fecundity or viability selection, and seldom results in the evolution of female display traits. Research on orthopterans has shown that complete sex role reversal (i.e. males choosy, females competitive) can occur when male parental investment limits female fecundity and reduces the potential rate of reproduction of males sufficiently to produce a female-biased operational sex ratio. By contrast, many systems exhibiting partial sex role reversal (i.e. males choosy and competitive) are not associated with elevated levels of male parental investment, reduced male reproductive rates, or reduced male bias in the operational sex ratio. Instead, large female mate quality variance resulting from factors such as strong last-male sperm precedence or large variance in female fecundity may select for both male choosiness and competitiveness in such systems. Thus, partial and complete sex role reversal do not merely represent different points along a continuum of increasing male parental investment, but may evolve via different evolutionary pathways.

Animals↗

PubMed2000

Voltammetry as a tool for monitoring micellar structural evolution?

Self-assembled systems such as micelles and liquid crystals are currently of interest as templates for the controlled formation of nanoscale structures. Knowledge of the mesophase structure, structural evolution, and interparticle interaction is of great importance in understanding the behavior of such systems especially for applications such as nanoreactors. Here, we compare the use of cyclic voltammetry, chronoamperometry, and the rotating disk electrode (RDE) for the determination of micellar hydrodynamic radii and show that only the steady-state RDE yields values directly comparable with nonelectrochemical techniques. The RDE is applied for the determination of cetyltrimethylammonium chloride micellar structure and observing micellar structural evolution as well as evaluating the usual intermicellar interactions. The results clearly show (a) the collapse of the micellar shear plane toward the hard-sphere surface with increasing electrolyte concentration, (b) the electrolyte-dependent spherical expansion of the micellar hard-spheres due to increasing aggregation (N) number, (c) the structural transition from spherical to rodlike micelles, and (d) micellar elongation. As well as structural evolution, the evolutionary changes in interaction processes are also observed, i.e. the transition from Coulombic interactions to excluded volume interaction. This paper describes in detail the voltammetric measurement of these processes and explicates the necessary experimental conditions for successful observation of micellar structural evolution.

Journal Article↗

PubMed1992

Oxygen evolution in the absence of the 33-kilodalton manganese-stabilizing protein.

There has been a considerable amount of controversy concerning the ability of photosystem II to evolve oxygen in the absence of the 33-kDa, manganese-stabilizing protein. Early reports indicated that some capacity for oxygen evolution existed in manganese-stabilizing protein-depleted membranes while more recent studies have suggested that the observed oxygen evolution activity arose from residual manganese-stabilizing protein present in the salt-washed preparations. In this paper, it is conclusively demonstrated that significant rates of steady-state oxygen evolution are observed in oxygen-evolving photosystem II membranes in the absence of detectable quantities of the manganese-stabilizing protein. More then 99% of the manganese-stabilizing protein was removed by either one CaCl2 or two NaCl-urea washes. The amount of manganese-stabilizing protein removed was quantified immunologically using mouse polyclonal antibodies. Oxygen evolution rates of 115-140 mumol of O2 (mg of Chl)-1 h-1 were observed in the NaCl-urea-washed preparations. These rates represent about 24% of the rate observed in untreated membranes [450-600 mumol of O2 (mg of Chl)-1 h-1]. Somewhat lower, although still significant rates were observed in the CaCl2-washed preparations. Optimal rates of oxygen-evolving activity in NaCl-urea-washed membranes which are devoid of the manganese-stabilizing protein required high concentrations of calcium and chloride.

Kinetics↗

PubMed2002

pH dependence of the four individual transitions in the catalytic S-cycle during photosynthetic oxygen evolution.

We have investigated the pH dependence for each individual redox transition in the S-cycle of the oxygen evolving complex (OEC) of photosystem II by electron paramagnetic resonance (EPR) spectroscopy. In the experiments, OEC is advanced to the appropriate S-state at normal pH. Then, the pH is rapidly changed, and a new flash is given. The ability to advance to the next S-state in the cycle at different pHs is determined by measurements of the decrease or increase of characteristic EPR signals from the OEC in different S-states. In some cases the measured EPR signals are very small (this holds especially for the S0 ML signal at pH >7.5 and pH <4.8). Therefore, we refrain from providing error limits for the determined pK's. Our results indicate that the S1 --> S2 transition is independent of pH between 4.1 and 8.4. All other S-transitions are blocked at low pH. In the acidic region, the pK's for the inhibition of the S2 --> S3, the S3 --> [S4] --> S0, and the S0 --> S1 transitions are about 4.0, 4.5, and 4.7, respectively. The similarity of these pK values indicates that the inhibition of the steady-state oxygen evolution in the acidic range, which occurs with pK approximately 4.8, is a consequence of similar pH blocks in three of the redox steps involved in the oxygen evolution. In the alkaline region, we report a clear pH block in the S3 --> [S4] --> S0 transition with a pK of about 8.0. Our study also indicates the existence of a pH block at very high pH (pK approximately 9.4) in the S2 --> S3 transition. The S0 --> S1 transition is not affected, at least up to pH 9.0. This suggests that the inhibition of the steady-state oxygen evolution, which occurs with a pK of 8.0, is dominated by the inhibition of the S3 --> [S4] --> S0 transition. Our results are obtained in the presence of 5% methanol (v/v). However, it is unlikely that the determined pK's are affected by the presence of methanol since our results also show that the pH dependence of the steady-state oxygen evolution is not affected by methanol. The results in the alkaline region are in good agreement with a model, which suggests that the redox potential of Y(Z*)/Y(Z) is directly affected by high pH. At high pH the Y(Z*)/Y(Z) potential becomes lower than that of S2/S1 and S3/S2. The acidic block, with a pK of 4-5 in three S-transitions, implies that the inhibition mechanism is similar, and we suggest that it reflects protonation of a carboxylic side chain in the proton relay that expels protons from the OEC.

Catalysis↗

PubMed2005

Characteristics of iodide activation and inhibition of oxygen evolution by photosystem II.

Oxygen evolution by photosystem II (PSII) is activated by chloride and other monovalent anions. In this study, the effects of iodide on oxygen evolution activity were investigated using PSII-enriched membrane fragments from spinach. In the absence of Cl(-), the dependence of oxygen evolution activity on I(-) concentration showed activation followed by inhibition in both intact PSII and NaCl-washed PSII, which lacked the PsbP and PsbQ subunits. Using a substrate inhibition model, the range of values of the Michaelis constant K(M) in intact PSII (0.5-1.5 mM) was smaller than that in NaCl-washed PSII (1.5-5 mM), whereas values of the inhibition constant K(I) in intact PSII (9-17 mM) were larger than those in NaCl-washed PSII (1-4 mM). Studies of I(-) inhibition of Cl(-)-activated oxygen evolution in intact PSII revealed that I(-) was primarily an uncompetitive inhibitor, with uncompetitive constant K(i)' = 37 mM and Cl(-)-competitive constant K(i) > 200 mM. This result indicated that the activating Cl(-) must be bound for inhibition to take place, which is consistent with the substrate inhibition model for I(-) activation. The S(2) state multiline and g = 4.1 EPR signals in NaCl-washed PSII were examined in the presence of 3 and 25 mM NaI, corresponding to I(-)-activated and I(-)-inhibited conditions, respectively. The two S(2) state signals were observed at both I(-) concentrations, indicating that I(-) substitutes for Cl(-) in formation of the signals and that advancement to the S(2) state was not prevented by high I(-) concentrations. A model is presented that incorporates the results of this study, including the action of both chloride and iodide.

Binding Sites↗

PubMed1998

The carboxyl-terminal tripeptide of the manganese-stabilizing protein is required for quantitative assembly into photosystem II and for high rates of oxygen evolution activity.

The extrinsic manganese stabilizing protein of photosystem II is required for Mn retention by the O2-evolving complex, accelerates the rate of O2 evolution, and protects photosytem II against photoinhibition. We report results from studies of the in vitro reconstitution of spinach photosytem II with recombinant manganese stabilizing protein with C-terminal deletions of two, three, and four amino acids. The deletions were the result of amber mutations introduced by site-directed mutagenesis. Removal of the C-terminal dipeptide (Glu-Gln) did not diminish the ability of the manganese stabilizing protein either to rebind to or to restore high rates of O2 evolution to photosystem II preparations depleted of the native protein. Deletion of the C-terminal tripeptide (Leu-Glu-Gln) resulted in weakened but specific binding of manganese stabilizing protein to photosystem II and minimal recovery of O2 evolution activity. Removal of the C-terminal tetrapeptide (Gln-Leu-Glu-Gln) eliminated the ability of the subunit to interact stably with all of its available binding sites on photosystem II, as evidenced by the fact that this mutant was totally inactive in restoring O2 evolution activity. Evidence is presented to indicate that these mutational effects on the binding and function of the manganese stabilizing protein may be due to major changes in tertiary structure. The truncation mutations lacking either the C-terminal tri- or tetrapeptide exhibit apparent size increases of 25 and 40%, respectively, when compared either to a mutant lacking the C-terminal dipeptide or to the wild-type protein.

Arabidopsis↗

PubMed2005

Enhanced coagulation due to evaporation and its effect on nanoparticle evolution.

A new explanation for the evolution of particles near a roadway is proposed. The explanation starts with data that suggest that small (<15 nm) liquid nanoparticles shed semivolatile organics (<C24) almost immediately upon emission. It is shown here that the shrinking of these particles enhances their rates of coagulation by over an order of magnitude, and this appears important in helping to explain particle evolution further downwind, as measured by two datasets, including one reported here, and as found with a three-dimensional numerical model used to simulate the data. Enhanced coagulation in isolated emission puffs may also affect evolution. Neither condensation, complete evaporation, coagulation alone, nor preferential small-particle dilution appears to explain the evolution.

Air Pollutants↗

PubMed2004

Photocatalytic H2 evolution reaction from aqueous solutions over band structure-controlled (AgIn)xZn2(1-x)S2 solid solution photocatalysts with visible-light response and their surface nanostructures.

(AgIn)(x)Zn(2(1-x))S(2) solid solutions between ZnS photocatalyst with a wide band gap and AgInS(2) with a narrow band gap showed photocatalytic activities for H(2) evolution from aqueous solutions containing sacrificial reagents, SO(3)(2)(-) and S(2)(-), under visible-light irradiation (lambda >or= 420 nm) even without Pt cocatalysts. Loading of the Pt cocatalysts improved the photocatalytic activity. Pt (3 wt %)-loaded (AgIn)(0.22)Zn(1.56)S(2) with a 2.3 eV band gap showed the highest activity for H(2) evolution, and the apparent quantum yield at 420 nm amounted to 20%. H(2) gas evolved at a rate of 3.3 L m(-2) x h(-1) under irradiation using a solar simulator (AM 1.5). The diffuse reflection and the photoluminescence spectra of the solid solutions shifted monotonically to a long wavelength side as the ratio of AgInS(2) to ZnS increased in the solid solutions. The photocatalytic H(2) evolution depended on the compositions as well as the photophysical properties. The dependence of the photophysical and photocatalytic properties upon the composition was mainly due to the change in the band position caused by the contribution of the Ag 4d and In 5s5p orbitals to the valence and conduction bands, respectively. It was found from SEM and TEM observations that the solid solutions partially had nanostep structures on their surfaces. The Pt cocatalysts were selectively photodeposited on the edge of the surface nanosteps. It was suggested that the specific surface nanostructure was effective for the suppression of recombination between photogenerated electrons and holes and for the separation of H(2) evolution sites from oxidation reaction sites.

Journal Article↗

PubMed2006

Particle-wire-tube mechanism for carbon nanotube evolution.

The synthesis of carbon nanotubes (CNTs) has been proved to be greatly promoted by vapor metal catalysts, but the fast reaction feature and the required high-temperature environment involved in CNT evolution usually make it difficult for an insight into the evolution mechanism. Here, we successfully freeze the synthetic reaction at intermediary stages and observe the detailed morphologies and structures of the obtained intermediates and various objects related to carbon nanotubes. It is unveiled that there is a kindred evolution linkage among carbon nanoparticles, nanowires, and nanotubes in the vapor catalyst-involved synthetic processes: tiny carbon nanoparticles first form from a condensation of gaseous carbon species and then self-assemble into nanowires driven by an anisotropic interaction, and the nanowires finally develop into nanotubes, as a consequence of particle coalescence and structural crystallization. The function of metals is to promote the anisotropic interactions between the nanoparticles and the structural crystallization. An annealing transformation of carbon nanoparticles into nanotubes is also achieved, which gives further evidence for the evolution mechanism.

Journal Article↗

PubMed2005

Zinc oxide nanostructures: morphology derivation and evolution.

Zinc oxide nanostructures of various types, including nanobelts, nanoplatelets, nanowires, and nanorods, have been synthesized via well-developed routes by many research groups. However, so far, the underlying mechanism for the morphology derivation and evolution of the nanostructures has not been elucidated in depth. In this article, we report the systematic investigation of the morphology evolution characteristics of ZnO nanostructures from dense rods to dense nanoplatelets, nanoplatelet flowers, dense nanobelt flowers, and nanowire flowers in an evaporation-physical transport-condensation approach. Through the use of crystal growth theory, the determining factors for the formation of different nanostructural morphologies were found to be gas-phase supersaturation and the surface energy of the growing surface planes. Other experimental parameters such as the temperature at the source and the substrate, the temperature difference and the distance between the source and the substrate, the heating rate of the furnace, the gas flow rate, the ceramic tube diameter, and the starting material are all correlated with supersaturation and impose an effect on the morphology evolution. This finding may have an important impact on the qualitative understanding of the morphology evolution of nanostructures and the achieving of desired nanostructures controllably.

Journal Article↗

PubMed2004

Thinking about the evolution of photosynthesis.

Photosynthesis is an ancient process on Earth. Chemical evidence and recent fossil finds indicate that cyanobacteria existed 2.5-2.6 billion years (Ga) ago, and these were certainly preceded by a variety of forms of anoxygenic photosynthetic bacteria. Carbon isotope data suggest autotrophic carbon fixation was taking place at least a billion years earlier. However, the nature of the earliest photosynthetic organisms is not well understood. The major elements of the photosynthetic apparatus are the reaction centers, antenna complexes, electron transfer complexes and carbon fixation machinery. These parts almost certainly have not had the same evolutionary history in all organisms, so that the photosynthetic apparatus is best viewed as a mosaic made up of a number of substructures each with its own unique evolutionary history. There are two schools of thought concerning the origin of reaction centers and photosynthesis. One school pictures the evolution of reaction centers beginning in the prebiotic phase while the other school sees reaction centers evolving later from cytochrome b in bacteria. Two models have been put forth for the subsequent evolution of reaction centers in proteobacteria, green filamentous (non-sulfur) bacteria, cyanobacteria, heliobacteria and green sulfur bacteria. In the selective loss model the most recent common ancestor of all subsequent photosynthetic systems is postulated to have contained both RC1 and RC2. The evolution of reaction centers in proteobacteria and green filamentous bacteria resulted from the loss of RC1, while the evolution of reaction centers in heliobacteria and green sulfur bacteria resulted from the loss of RC2. Both RC1 and RC2 were retained in the cyanobacteria. In the fusion model the most recent common ancestor is postulated to have given rise to two lines, one containing RC1 and the other containing RC2. The RC1 line gave rise to the reaction centers of heliobacteria and green sulfur bacteria, and the RC2 line led to the reaction centers of proteobacteria and green filamentous bacteria. The two reaction centers of cyanobacteria were the result of a genetic fusion of an organism containing RC1 and an organism containing RC2. The evolutionary histories of the various classes of antenna/light-harvesting complexes appear to be completely independent. The transition from anoxygenic to oxygenic photosynthesis took place when the cyanobacteria learned how to use water as an electron donor for carbon dioxide reduction. Before that time hydrogen peroxide may have served as a transitional donor, and before that, ferrous iron may have been the original source of reducing power.

Journal Article↗

PubMed1976

Localization of inhibition by adenosine diphosphate of phosphoglycerate-dependent oxygen evolution in a reconstituted chloroplast system.

ADP was shown to inhibit phosphoglycerate-dependent O2 evolution in a simplified reconstituted chloroplast system containing 3-phosphoglycerate kinase and triose phosphate dehydrogenase. Rates of O2 evolution in the simplified system are comparable with those obtained by using stromal protein rather than purified enzymes. ADP does not inhibit O2 evolution with glycerate 1,3-biphosphate as substrate nor does it inhibit triose phosphate dehydrogenase. The inhibitory effect of ADP is attributed to an increase in the rate of conversion of glycerate biphosphate into phosphoglycerate. The results are discussed in terms of control by ADP of phosphoglycerate-dependent oxygen evolution.

Adenosine Diphosphate↗

PubMed1979

Measurement in vivo of hydrogenase-catalysed hydrogen evolution in the presence of nitrogenase enzyme in cyanobacteria.

A method was devised that allows measurement in vivo of hydrogenase-catalysed H2 evolution from the cyanobacterium Anabaena cylindrica, independent of nitrogenase activity, which is also present. Addition of low concentrations of reduced Methyl Viologen (1-10mM) to intact heterocystous filaments of the organism resulted in H2 evolution, but produced conditions giving total inhibition of nitrogenase (acetylene-reducing and H2-evolving) activity. That the H2 formed under these conditions was not contributed to by nitrogenase was also supported by the observation that its rate of formation was similar in the dark or with Ar replaced by N2 in the gas phase, and also in view of the pattern of H2 evolution at very low Methyl Viologen concentrations. Conclusive evidence that the H2 formed in the presence of Methyl Viologen was solely hydrogenase-mediated was its evolution even from nitrogenase-free (non-heterocystous) cultures; by contrast 'uptake' hydrogenase activity in such cultures was greatly decreased. The hydrogenase activity was inhibited by CO and little affected by acetylene. Finally the hydrogenase activity was shown to be relatively constant at different stages during the batch growth of the organism, as opposed to nitrogenase activity, which varied.

Acetylene↗