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PubMed2005

Nonlinear enhancement of oxygen evolution in thylakoid membranes: modeling the effect of light intensity and beta-cyclodextrin concentration.

Electron transport through photosystem II, measured as oxygen evolution (OE), was investigated in isolated thylakoid membranes treated with beta-cyclodextrin (beta-CD, a cyclic oligosaccharide constituted of seven alpha-d-glucose residues linked by alpha-1,4 glycosidic bonds) and irradiated with white light of variable intensity. First, we found that the light-response curves of oxygen evolution are well fitted with a hyperbolic function, the shape of which is not affected by the beta-CD concentration. Second, we showed that under conditions of irradiation with white light of saturating intensity ( approximately 5000 mumol of photons/m(2).s) beta-CD enhances the oxygen evolution in the thylakoid membranes according to a sigmoid function displaying a sharp inflection point, or transition. Unexpectedely, this beta-CD effect is not observed at irradiances of less than approximately 300 mumol of photons/m(2).s. We attempted a theoretical analysis of the combined effect of irradiance and beta-CD concentration on oxygen evolution (OE(th)). For this purpose, the effect of irradiance (I) was modeled with a hyperbola (i) and the beta-CD concentration (C) contribution with a Hill equation, that is, a sigmoid function (ii). The mathematical simulations generated the following general expressions: (i) OE(th) = [OE(max)(0) G(1)(C)]I/[L(1/2)(0) G(2)(C) + I] and (ii) G(i)()(C) = 1 + p[C(n)()/(K(1/2)(n)() + C(n)())], where OE(max)(0) is the OE maximum (OE(max)) in the absence of beta-CD, L(1/2)(0) is the photon flux density giving OE(max)/2 in the absence of beta-CD, G(1)(C) or G(2)(C) is obtained from G(i)()(C) where i is 1 or 2, n is the Hill coefficient, p is a parameter to account for the beta-CD-mediated maximum OE increase, and K(1/2) is the beta-CD concentration giving half-maximal OE activity. The results of the calculations yielded the expression (iii) OE(th) = 151[1 + 3.3C(4.8)/(13.1(4.8) + C(4.8))]I/{97.5[1 + 5.2C(7.8)/(14.8(7.8) + C(7.8))] + I} which agrees well with the experimental data for a broad range of I and C. Note that, for C = 0, eq iii reverts to the light-response curve of oxygen evolution in the absence of beta-CD. We conclude that eq iii is a good approximation of the combined effect of irradiance and beta-CD concentration, meaning that the model has a significant value for predicting the outcome of associated photochemical and biochemical reactions.

Electron Transport↗

PubMed1998

Long-term administration of G-CSF for aplastic anaemia is closely related to the early evolution of monosomy 7 MDS in adults.

There is an increasing incidence of the evolution of myelodysplastic syndrome (MDS) from aplastic anaemia (AA) with immunosuppressive treatment. In paediatric patients G-CSF is also reported to increase MDS evolution, but this process is not precisely understood in children or in adults. Therefore risk factors of MDS evolution in adults are evaluated here. Of 72 patients, five developed MDS. In 47 patients without cyclosporine (CyA) or antithymocyte globulin (ATG) therapy, only one developed MDS with trisomy 8, 242 months after diagnosis. But of 25 patients treated with either CyA or ATG, four developed monosomy 7 MDS within 3 years. Of these 25 patients, 18 were treated with G-CSF and the four patients (22.2%) who developed MDS were found in this group. The cumulative dose and the duration of G-CSF administration were significantly elevated in patients who developed MDS when compared with those who did not, 822.3 +/- 185.0 v 205.4 +/- 25.5 microg/kg (P<0.05) and 187.5 +/- 52.5 v 72.0 +/- 24.6 d (P<0.002), respectively. However these two values for CyA did not differ significantly. Statistically, treatment with CyA, G-CSF and combined G-CSF and CyA were significantly related to MDS evolution. The administration of G-CSF for more than a year was the most important factor (P=0.00). These results suggested that a close relationship exists between G-CSF and subsequent monosomy 7 MDS from AA in adults who receive immunosuppressive therapy. Long-term administration of G-CSF should be prohibited in order to prevent MDS evolution.

Adolescent↗

PubMed2006

Relative Boltzmann entropy, evolution equations for fluctuations of thermodynamic intensive variables, and a statistical mechanical representation of the zeroth law of thermodynamics.

Generalized thermodynamics or extended irreversible thermodynamics presumes the existence of thermodynamic intensive variables (e.g., temperature, pressure, chemical potentials, generalized potentials) even if the system is removed from equilibrium. It is necessary to properly understand the nature of such intensive variables and, in particular, of their fluctuations, that is, their deviations from those defined in the extended irreversible thermodynamic sense. The meaning of temperature is examined by means of a kinetic theory of macroscopic irreversible processes to assess the validity of the generalized (or extended) thermodynamic method applied to nonequilibrium phenomena. The Boltzmann equation is used for the purpose. Since the relative Boltzmann entropy has been known to be intimately related to the evolution of the aforementioned fluctuations in the intensive thermodynamic variables, we derive the evolution equations for such fluctuations of intensive variables to lay the foundation for investigating the physical implications and evolution of the relative Boltzmann entropy, so that the range of validity of the thermodynamic theory of irreversible processes can be elucidated. Within the framework of this work, we examine a special case of the evolution equations for the aforementioned fluctuations of intensive variables, which also facilitate investigation of the molecular theory meaning of the zeroth law of thermodynamics. We derive an evolution equation describing the relaxation of temperature fluctuations from its local value and present a formula for the temperature relaxation time.

Journal Article↗

PubMed2006

Codon-usage bias versus gene conversion in the evolution of yeast duplicate genes.

Many Saccharomyces cerevisiae duplicate genes that were derived from an ancient whole-genome duplication (WGD) unexpectedly show a small synonymous divergence (K(S)), a higher sequence similarity to each other than to orthologues in Saccharomyces bayanus, or slow evolution compared with the orthologue in Kluyveromyces waltii, a non-WGD species. This decelerated evolution was attributed to gene conversion between duplicates. Using approximately 300 WGD gene pairs in four species and their orthologues in non-WGD species, we show that codon-usage bias and protein-sequence conservation are two important causes for decelerated evolution of duplicate genes, whereas gene conversion is effective only in the presence of strong codon-usage bias or protein-sequence conservation. Furthermore, we find that change in mutation pattern or in tDNA copy number changed codon-usage bias and increased the K(S) distance between K. waltii and S. cerevisiae. Intriguingly, some proteins showed fast evolution before the radiation of WGD species but little or no sequence divergence between orthologues and paralogues thereafter, indicating that functional conservation after the radiation may also be responsible for decelerated evolution in duplicates.

Codon↗

PubMed1971

Interconnected patterns of biogeography and evolution.

Analysis of the fauna of the carabid beetles of New Guinea reveals both a broad dispersal pattern and a local turnover pattern that together fit into a world-wide pattern of successive dispersals and replacements that run from large to small areas and from more to less favorable climates. This pattern coincides broadly with a world-wide pattern of species numbers. Evolution by group selection, proceeding most rapidly and effectively where species are most numerous, connects the patterns and can supply the force that gives direction to the dispersal pattern. Directional change at any level of complexity involves movement that results in the formation of diverse groups of units (which are themselves groups of smaller units) and differential survival. This process-generalized group selection-has been continuous from chemical evolution on the earth's surface, through the origin of life, and into successive interacting levels of organic evolution. A corollary is that evolution should make situations favorable to itself, by group selection, and has probably done so in (for example) tropical rain forest, where new information about group evolution may be sought.

Journal Article↗

PubMed1996

Evolution of chlorophyll and bacteriochlorophyll: the problem of invariant sites in sequence analysis.

Competing hypotheses seek to explain the evolution of oxygenic and anoxygenic processes of photosynthesis. Since chlorophyll is less reduced and precedes bacteriochlorophyll on the modern biosynthetic pathway, it has been proposed that chlorophyll preceded bacteriochlorophyll in its evolution. However, recent analyses of nucleotide sequences that encode chlorophyll and bacteriochlorophyll biosynthetic enzymes appear to provide support for an alternative hypothesis. This is that the evolution of bacteriochlorophyll occurred earlier than the evolution of chlorophyll. Here we demonstrate that the presence of invariant sites in sequence datasets leads to inconsistency in tree building (including maximum-likelihood methods). Homologous sequences with different biological functions often share invariant sites at the same nucleotide positions. However, different constraints can also result in additional invariant sites unique to the genes, which have specific and different biological functions. Consequently, the distribution of these sites can be uneven between the different types of homologous genes. The presence of invariant sites, shared by related biosynthetic genes as well as those unique to only some of these genes, has misled the recent evolutionary analysis of oxygenic and anoxygenic photosynthetic pigments. We evaluate an alternative scheme for the evolution of chlorophyll and bacteriochlorophyll.

Bacteriochlorophylls↗

PubMed2004

Correlated evolution in fig pollination.

This is the first comparative study of correlated evolution between figs (Ficus species, Moraceae) and their pollinators (Hymenoptera: Agaoninae) based on molecular phylogenies of both lineages. Fig relationships based on the internal transcribed spacer region (ITS) of nuclear ribosomal DNA and pollinator relationships inferred from mitochondrial cytochrome oxidase I (COI) sequences enabled the study of correlated evolution based on molecular phylogenies for the largest set of interacting species ever compared. Comparative methods have been applied to tests of adaptation, but the application of these methods in tests of coadaptation, defined as reciprocal evolutionary change in interacting lineages, has received less attention. I have extended tests of correlated evolution between two traits along a phylogeny to the case of interacting lineages, where two traits may or may not share a common phylogenetic history. Independent contrasts and phylogenetic autocorrelation rejected the null hypothesis that trait correlations within lineages are stronger than trait correlations between interacting lineages. Fig style lengths and pollinator ovipositor lengths, for example, were more highly correlated than were pollinator body size and ovipositor length. Mutualistic interactions between figs and their pollinators illustrate the novel ways in which phylogenies and comparative methods can detect patterns of correlated evolution. The most outstanding evidence of correlated evolution between these obligate mutualists is that interacting trait correlations are stronger than within-lineage allometric relationships.

Adaptation, Biological↗

PubMed1998

Effect of some physiological factors on nitrogenase activity and nitrogenase mediated hydrogen evolution by mixed microbial culture.

Fermentative H2 evolution, nitrogenase activity (acetylene reduction) and nitrogenase mediated H2 evolution was studied in free cells of mixed microbial population of H2 producers. At 3% glucose level, the cells produced 8.35 l H2/mol glucose utilized. The role of nitrogenase system in H2 generation was evident by derepressed nitrogenase activity (0.46 nmoles C2H4 produced/mg protein/h) under defined in vitro conditions. For maximum expression of the activity, the cells required preactivation under anaerobic conditions by incubating at 40 degrees C for 20-24 h with 0.2% glucose in the culture medium. At an O2 level of more than 0.25%, the acetylene reduction activity decreased significantly and could not be detected at a level of 20%. Nitrogenase activity development was higher at acetylene: inoculum ratio between 4.2-6.25. H2 evolution was lower when the mixed cells were incubated under an atmosphere of 10% C2H2 and 5% CO gas. This decrease in H2 evolution was also evident at 2.5-6.5 mM NaNO3 and KNO3 concentrations in the liquid culture medium thus establishing more than 50% H2 evolution through nitrogenase.

Acetylene↗

PubMed2000

Metallicity Evolution in the Early Universe.

Observations of the damped Lyalpha systems provide direct measurements on the chemical enrichment history of neutral gas in the early universe. In this Letter, we present new measurements for four damped Lyalpha systems at high redshift. Combining these data with [Fe/H] values culled from the literature, we investigate the metallicity evolution of the universe from z approximately 1.5 to 4.5. Contrary to our expectations and the predictions of essentially every chemical evolution model, the N(H i)-weighted mean [Fe/H] metallicity exhibits minimal evolution over this epoch. For the individual systems, we report tentative evidence for an evolution in the unweighted [Fe/H] mean and the scatter in [Fe/H], with the higher redshift systems showing lower scatter and lower typical [Fe/H] values. We also note that no damped Lyalpha system has &sqbl0;Fe&solm0;H&sqbr0;<-2.7 dex. Finally, we discuss the potential impact of small number statistics and dust on our conclusions and consider the implications of these results on chemical evolution in the early universe.

Journal Article↗

PubMed1997

Numerical calculation of energy deposition by high-energy electron beams: III-B. Improvements to the 6D phase space evolution model.

The phase space evolution model of Huizenga and Storchi, Morawska-Kaczyńska and Huizenga and Janssen et al has been modified to (i) allow application on currently available computer equipment with limited memory (128 Megabytes) and (ii) allow 3D dose calculations based on 3D computer tomographic patient data. This is a further development aimed at the use of the phase space evolution model in radiotherapy electrons beam treatment planning. The first modification regards the application of depth evolution of the phase space state combined with an alternative method to transport back-scattered electrons. This depth evolution method requires of the order of 15 times less computer memory than the energy evolution method. Results of previous and new electron transport methods are compared and show that the new electron transport method for back-scattered electrons hardly affects the accuracy of the calculated dose distributions. The second modification regards the simulation of electron transport through tissues with varying densities by applying distributed electron transport through similarly composed media with a limited number of fixed densities. Results of non-distributed and distributed electron transport are compared and show that the distributed electron transport method hardly affects the accuracy of the calculated dose distributions. It is also shown that the results of the new dose distribution calculations are still in good agreement with and require significantly less computation time than results obtained with the EGS4 Monte Carlo method.

Electrons↗

PubMed2002

Photosynthetic oxygen evolution at low water potential in leaf discs lacking an epidermis.

Land plants encountering low water potentials (low psiw) close their stomata, restricting CO2 entry and potentially photosynthesis. To determine the impact of stomatal closure, photosynthetic O2 evolution was investigated in leaf discs from sunflower (Helianthus annuus L.) plants after removing the lower epidermis at low psiw. Wounding was minimal as evidenced by O2 evolution nearly as rapid as that in intact discs. O2 evolution was maximal in 1% CO2 in the peeled discs and was markedly inhibited when psiw was below -1.1 MPa. CO2 entered readily at all psiw, as demonstrated by varying the CO2 concentration. Results were the same whether the epidermis was removed before or after low psiw was imposed. Due to the lack of an epidermis and ready movement or CO2 through the mesophyll, the loss in O2 evolving activity was attributed entirely to photosynthetic metabolism. Intact leaf discs showed a similar loss in activity when measured at a CO2 concentration of 5%, which supported maximum O2 evolution at low psiw. In 1% CO2, however, O2 evolution at low psiw was below the maximum, presumably because stomatal closure restricted CO2 uptake. The inhibition was larger than in peeled discs at psiw between -1 and -1.5 MPa but became the same as in peeled discs at lower psiw. Therefore. as photosynthesis began to be inhibited by metabolism at low psiw, stomatal closure added to the inhibition. As psiw became more negative, the inhibition became entirely metabolic.

Carbon Dioxide↗

PubMed2004

Effects of insect population size on evolution of resistance to transgenic crops.

Models of the evolution of insect resistance to transgenic crops have often assumed that population size is infinite or that carrying capacity is fixed. To evaluate potential effects of population size on resistance evolution, we conducted sensitivity analyses by using a stochastic, spatially explicit model based partly on the interaction between pink bollworm and Bacillus thuringiensis (Bt) cotton. We examined interactions of carrying capacity, region size, dispersal, and percentage of fields planted with Bt cotton. The median and variance in the time to resistance decreased as region size increased, regardless of carrying capacity. This occurred because larger regions were more likely to have at least one field in which resistance evolved rapidly and served as a source from which resistance spread throughout the region. Carrying capacity significantly affected the median time to resistance with 75% of fields planted with Bt cotton, but not with 50% Bt cotton. In contrast, carrying capacity significantly influenced the variance in the time to resistance with 50% Bt cotton, but not with 75% Bt cotton. We also found resistance evolution was affected by interactions between carrying capacity, dispersal, and the percentage of fields planted with Bt cotton. The high variability observed in our simulations indicates that factors affecting stochastic events can play an important role in the evolution of resistance. Because population size determines the extent to which stochastic events are important, reasonable estimates of population size are essential for devising robust models of resistance evolution.

Animals↗

PubMed1977

Protection against carbon tetrachloride-induced lipid peroxidation in the rat by dietary vitamin E, selenium, and methionine as measured by ethane evolution.

Dietary vitamin E, selenium (Se), and methionine were tested for their ability to inhibit carbon tetrachloride (CCL4)-induced lipid peroxidation. Peroxidation, in vivo, was monitored by the evolution of ethane, an autoxidation product of omega-3-unsaturated fatty acids. Weanling rats were fed a basal diet low in vitamin E, Se, and sulfur-containing amino acids, or diets individually supplemented with these factors. After 3 to 7 weeks, the rats were injected with CCL4 (ip) and ethane was collected for 9 hours. Cumulative ethane evolution was increased by CCl4 in all groups. Vitamin E, Se, and methionine reduced ethane evolution from CCl4-treated rats by 82%, 74%, and 60%, respectively. The toxicity of CCl4 was decreased in correlation with ethane evolution. Thus, methionine and Se, probably by maintaining intracellular glutathione and glutathione peroxidase, protected against CCl4-induced lipid peroxidation, as did vitamin E. Substitution of cod liver oil, which is rich in omega-3-unsaturated fat, for lard in the basal diet increased CCl4-induced ethane evolution six-fold. Relative inhibition by the dietary supplements was not changed. Thus, the feeding of cod liver oil greatly increased ethane production which facilitated the detection and measurement of lipid peroxidation in vivo.

Animals↗

PubMed2006

Patterns of intron loss and gain in plants: intron loss-dominated evolution and genome-wide comparison of O. sativa and A. thaliana.

Numerous previous studies have elucidated 2 surprising patterns of spliceosomal intron evolution in diverse eukaryotes over the past roughly 100 Myr. First, rates of recent intron gain in a wide variety of eukaryotic lineages have been surprisingly low, far too low to explain modern intron densities. Second, intron losses have outnumbered intron gains over a variety of lineages. For several reasons, land plants might be expected to have comparatively high rates of intron gain and thus to represent a possible exception to this pattern. However, we report several studies that indicate low rates of intron gain and an excess of intron losses over intron gains in a variety of plant lineages. We estimate that intron losses have outnumbered intron gains in recent evolution in Arabidopsis thaliana (roughly 12.6 times more losses than gains), Oryza sativa (9.8 times), the green alga Chlamydomonas reinhardtii (5.1 times), and the Bigelowiella natans nucleomorph, an enslaved green algal nucleus (2.8 times). We estimate that during recent evolution, A. thaliana and O. sativa have experienced very low rates of intron gain of around one gain per gene per 2.6-8.0 billion years. In addition, we compared 8,258 pairs of putatively orthologous A. thaliana-O. sativa genes. We found that 5.3% of introns in conserved coding regions are species-specific. Observed species-specific A. thaliana and O. sativa introns tend to be exact and to lie adjacent to each other along the gene, in a pattern suggesting mRNA-mediated intron loss. Our results underscore that low intron gain rates and intron number reduction are common features of recent eukaryotic evolution. This pattern implies that rates of intron creation were higher during earlier periods of evolution and further focuses attention on the causes of initial intron proliferation.

Amino Acid Sequence↗

PubMed1998

Hydrogen evolution by direct electron transfer from photosystem I to hydrogenases.

H2 evolution by direct electron transfer from the dithionite-reduced photosystem I (PSI) complex to both hydrogenase I and hydrogenase II from Clostridium pasteurianum was observed. Evidence indicates that the electron carriers on PSI that transfer electrons to hydrogenase in this system are the FA/FB iron-sulfur clusters on the PsaC polypeptide, the terminal bound electron acceptors in PSI. Light-dependent H2 evolution was also observed, using high potential electron donors to PSI, from a combination of hydrogenase I and either solubilized purified PSI or thylakoids. Mediators capable of transferring electrons from the PSI complex to hydrogenase were not necessary for H2 evolution, indicating again that the mechanism of H2 evolution is direct electron transfer from PSI to hydrogenase, and that this can occur with light-reduced as well as chemically reduced PSI, and with PSI in thylakoids as well as the solubilized complex. Light-dependent H2 evolution was also observed from a mixture of thylakoids and the oxygen-resistant hydrogenase of Rhodococcus sp. MR11. These results suggest that direct electron transfer from PSI to hydrogenase could be engineered to occur in vivo in a photosynthetic organism to create an organism that would efficiently produce H2 from H2O.

Clostridium↗

PubMed2002

Acute megakaryoblastic leukemia after transient myeloproliferative disorder with clonal karyotype evolution in a phenotypically normal neonate.

We report a case of transient myeloproliferative disorder (TMD) in a neonate without features of Down syndrome (DS) with clonal karyotype evolution, after apparent spontaneous resolution of TMD, but eventually progressing to acute megakaryoblastic leukemia (AMKL). The patient had petechiae, thrombocytopenia, and blastemia. Trisomy 21 with a satellited Y chromosome (Yqs) was found in proliferating blasts. A stimulated peripheral blood culture confirmed the constitutional origin of the Yqs, but did not reveal the presence of any trisomic 21 cell. By the age of 3 months, clonal chromosome evolution in the form of an interstitial deletion of the long-arm of chromosome 13 [del(13)(q13q31)] was detected along with trisomy 21 in unstimulated bone marrow cultures. However, remission was achieved without treatment at the age of 4 months. Trisomy 21 and del(13)(q13q31) were not identified in either cytogenetics or fluorescence in situ hybridization studies at that time. The child was asymptomatic until the age of 20 months when anemia and thrombocytopenia prompted a bone marrow biopsy, revealing changes consistent with AMKL. The remission proceeded by clonal karyotype evolution in a neonate with TMD demonstrates that clonal karyotype evolution does not indicate an immediately progressive disease. However, the development of AMKL after TMD in this case illustrates the increased risk for leukemia in TMD cases, even without DS. The gradual clonal evolution of the blasts in our patient suggests that "multiple hits" oncogenesis applies to TMD progression to acute leukemia.

Bone Marrow↗

PubMed1969

Determination of the Rate of CO(2) Evolution by Green Leaves in Light.

The rate of CO(2) evolution in light by green leaves was determined by 2 methods in a closed system of gas analysis and by measuring the amount of CO(2) evolved into a CO(2) free air stream in an open system. All methods gave similar results under comparable conditions.A light stimulated CO(2) evolution from green leaves was found in all the plant species studied except corn where there was no apparent CO(2) evolution in the light.The magnitude of CO(2) evolution in light was markedly dependent on air flow rate and light intensity. At high light intensity and high flow rate, the rate of CO(2) evolution from green leaves was 1.4 to 1.7 times greater than that in darkness.

Journal Article↗

PubMed1975

H(2) metabolism in photosynthetic organisms: I. Dark h(2) evolution and uptake by algae and mosses.

Dark H(2) metabolism was studied in marine and fresh water red algae, the green alga, Chlamydomonas, and mosses. A time variable and temperature-sensitive anaerobic incubation was required prior to H(2) evolution. H(2) evolution was sensitive to disalicylidenepropanediamine. An immediate H(2) uptake was observed in these algae. Immediate dark H(2) uptake but no evolution was observed in the mosses.A cell-free hydrogenase preparation was obtained from anaerobically adapted Chlamydomonas reinhardii by means of sonic oscillation. The hydrogenase was not sedimented at 100,000g. It catalyzed the reduction of methylene blue, p-benzoquinone, NAD, NADP, but not spinach ferredoxin. H(2) evolution was noted with dithionite and with reduced methyl viologen as donors but not with reduced spinach ferredoxin. Similarly, hydrogenase activities were not affected by disalicylidenepropanediamine. The pH optima for H(2) evolution and for H(2) uptake were 7.2 and 7.5 to 9.5, respectively. Extracts prepared from the anaerobically adapted red alga, Chondrus crispus, and the moss, Leptobryum pyriforme, consumed but did not evolve H(2). Uptake was slightly stimulated by methylene blue. It is proposed that red algae and mosses appear to metabolize H(2) by a different pathway than Chlamydomonas.

Journal Article↗