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PubMed1987

Klebsiella pneumoniae nitrogenase. Inhibition of hydrogen evolution by ethylene and the reduction of ethylene to ethane.

Ethylene (C2H4) inhibited H2 evolution by the Mo-containing nitrogenase of Klebsiella pneumoniae. The extent of inhibition depended on the electron flux determined by the ratio of Fe protein (Kp2) to MoFe protein (Kp1) with KiC2H4 = 409 kPa ([Kp2]/[Kp1] = 22:1) and KC2H4i = 88 kPa ([Kp1]/[Kp2] = 21:1) at 23 degrees C at pH 7.4. At [Kp2]/[Kp1] = 1:1, inhibition was minimal with C2H4 (101 kPa). Extrapolation of data obtained when C2H4 was varied from 60 to 290 kPa indicates that at infinite pressure of C2H4 total inhibition of H2 evolution should occur. C2H4 inhibited concomitant S2O4(2-) oxidation to the same extent that it inhibited H2 evolution. Although other inhibitors of total electron flux such as CN- and CH3NC uncouple MgATP hydrolysis from electron transfer, C2H4 did not affect the ATP/2e ratio. Inhibition of H2 evolution by C2H4 was not relieved by CO. C2H4 was reduced to C2H6 at [Kp2]/[Kp1] ratios greater than or equal to 5:1 in a reaction that accounted for no more than 1% of the total electron flux. These data are discussed in terms of the chemistry of alkyne and alkene reduction on transition-metal centres.

Dithionite↗

PubMed1972

Nonmathematical models for evolution of altruism, and for group selection (peck order-territoriality-ant colony-dual-determinant model-tri-determinant model).

Mathematical biologists have failed to produce a satisfactory general model for evolution of altruism, i.e., of behaviors by which "altruists" benefit other individuals but not themselves; kin selection does not seem to be a sufficient explanation of nonreciprocal altruism. Nonmathematical (but mathematically acceptable) models are now proposed for evolution of negative altruism in dual-determinant and of positive altruism in tri-determinant systems. Peck orders, territorial systems, and an ant society are analyzed as examples. In all models, evolution is primarily by individual selection, probably supplemented by group selection. Group selection is differential extinction of populations. It can act only on populations preformed by selection at the individual level, but can either cancel individual selective trends (effecting evolutionary homeostasis) or supplement them; its supplementary effect is probably increasingly important in the evolution of increasingly organized populations.

Animals↗

PubMed1992

Femtosecond spectral evolution of the excited state of bacterial reaction centers at 10 K.

The femtosecond spectral evolution of reaction centers of Rhodobacter sphaeroides R-26 was studied at 10 K. Transient spectra in the near infrared region, obtained with 45-fs pulses (pump pulses centered at 870 nm and continuum probe pulses), were analyzed with associated kinetics at specific wavelengths. The t = 0-fs transient spectrum is very rich in structure; it contains separate induced bands at 807 and 796 nm and a bleaching near 760 nm, reflecting strong changes in interaction between all pigments upon formation of the excited state. A complex spectral evolution in the 800-nm region, most notably the bleaching of the 796-nm band, takes place within a few hundred femtosecond--i.e., on a time scale much faster than electron transfer from the primary donor P to the bacteriopheophytin acceptor HL. The remarkable initial spectral features and their evolution are presumably related to the presence of HL, as they were not observed in the DLL mutant of Rhodobacter capsulatus, which lacks this pigment. A simple linear reaction scheme with an intermediate state cannot account for our data; the initial spectral evolution must reflect relaxation processes within the excited state. The importance for primary photochemistry of long distance interactions in the reaction center is discussed.

Cold Temperature↗

PubMed2004

Rapid evolution of beta-glucuronidase specificity by saturation mutagenesis of an active site loop.

Protein engineers have widely adopted directed evolution as a design algorithm, but practitioners have not come to a consensus about the best method to evolve protein molecular recognition. We previously used DNA shuffling to direct the evolution of Escherichia coli beta-glucuronidase (GUS) variants with increased beta-galactosidase activity. Epistatic (synergistic) mutations in amino acids 557, 566, and 568, which are part of an active site loop, were identified in that experiment (Matsumura, I., and Ellington, A. D. (2001) J. Mol. Biol. 305, 331-339). Here we show that site saturation mutagenesis of these residues, overexpression of the resulting library in E. coli, and high throughput screening led to the rapid evolution of clones exhibiting increased activity in reactions with p-nitrophenyl-beta-d-xylopyranoside (pNP-xyl). The xylosidase activities of the 14 fittest clones were 30-fold higher on average than that of the wild-type GUS. The 14 corresponding plasmids were pooled, amplified by long PCR, self-ligated with T4 DNA ligase, and transformed into E. coli. Thirteen clones exhibiting an average of 80-fold improvement in xylosidase activity were isolated in a second round of screening. One of the evolved proteins exhibited a approximately 200-fold improvement over the wild type in reactivity (k(cat)/K(m)) with pNP-xyl, with a 290,000-fold inversion of specificity. Sequence analysis of the 13 round 2 isolates suggested that all were products of intermolecular recombination events that occurred during whole plasmid PCR. Further rounds of evolution using DNA shuffling and staggered extension process (StEP) resulted in modest improvement. These results underscore the importance of epistatic interactions and demonstrate that they can be optimized through variations of the facile whole plasmid PCR technique.

Algorithms↗

PubMed1999

Evolution of Dust Extinction and Supernova Cosmology.

We have made a quantitative calculation for the systematic evolution of the average extinction by interstellar dust in host galaxies of high-redshift Type Ia supernovae by using a realistic model of photometric and chemical evolution of galaxies and supernova rate histories in various galaxy types. We find that the average B-band extinction at z approximately 0.5 is typically 0.1-0.2 mag larger than the present value, under a natural assumption that dust optical depth is proportional to gas column density and gas metallicity. This systematic evolution causes average reddening with E(B-V&parr0; approximately 0.025-0.05 mag with the standard extinction curve, and this is comparable with the observational uncertainty of the reddening of high-redshift supernovae. Therefore, our result does not contradict the observations that show no significant reddening in high-z supernovae. However, the difference in apparent magnitude between an open universe and a Lambda-dominated flat universe is only approximately 0.2 mag at z approximately 0.5, and hence this systematic evolution of extinction should be taken into account in a reliable measurement of cosmological parameters. Considering this uncertainty, we show that it is difficult to discriminate between open and Lambda-dominated flat cosmologies from the current data.

Journal Article↗

PubMed2000

Large Magellanic Cloud Planetary Nebula Morphology: Probing Stellar Populations and Evolution.

Planetary nebulae (PNe) in the Large Magellanic Cloud (LMC) offer the unique opportunity to study both the population and evolution of low- and intermediate-mass stars, by means of the morphological type of the nebula. Using observations from our LMC PN morphological survey, and including images available in the Hubble Space Telescope Data Archive and published chemical abundances, we find that asymmetry in PNe is strongly correlated with a younger stellar population, as indicated by the abundance of elements that are unaltered by stellar evolution (Ne, Ar, and S). While similar results have been obtained for Galactic PNe, this is the first demonstration of the relationship for extragalactic PNe. We also examine the relation between morphology and abundance of the products of stellar evolution. We found that asymmetric PNe have higher nitrogen and lower carbon abundances than symmetric PNe. Our two main results are broadly consistent with the predictions of stellar evolution if the progenitors of asymmetric PNe have on average larger masses than the progenitors of symmetric PNe. The results bear on the question of formation mechanisms for asymmetric PNe-specifically, that the genesis of PNe structure should relate strongly to the population type, and by inference the mass, of the progenitor star and less strongly on whether the central star is a member of a close binary system.

Journal Article↗

PubMed2003

In vitro evolution of proteins for drug development.

Thanks to biotechnology, proteins are becoming increasingly important tools to fight disease, both as therapeutics in their own right and as catalysts for the synthesis of small molecule drugs. However, the properties of these proteins are not necessarily optimal for their intended tasks. In vitro evolution is a set of technologies useful to address their shortcomings. Moreover, in vitro evolution can help illuminate natural evolutionary pathways, thus potentially enabling prediction of drug resistance evolution. We consider here recent developments in the area of in vitro evolution, as well as its application to proteins of interest to medical science.

Biological Assay↗

PubMed2003

Conventional and magnetization transfer MRI predictors of clinical multiple sclerosis evolution: a medium-term follow-up study.

The correlation between conventional MRI lesion load accumulation and multiple sclerosis clinical evolution is only modest. The assessment of brain parenchymal volume and of its changes over time may provide adjunctive MRI markers reflecting the more disabling aspects of multiple sclerosis pathology. Magnetization transfer (MT) MRI is sensitive to 'occult' multiple sclerosis-related brain damage and might also contribute to overcome the clinical/MRI paradox. In this study, we assessed the value of conventional and MT MRI-derived metrics in predicting the medium-term clinical evolution of patients with different multiple sclerosis phenotypes. We studied 73 patients, with relapsing-remitting multiple sclerosis (n = 34), secondary progressive multiple sclerosis (n = 19) and clinically isolated syndromes suggestive of multiple sclerosis (n = 20), and 16 healthy subjects. Brain dual-echo, T1-weighted (only in patients) and MT MRI scans were obtained at baseline and after 12 months. T2-hyperintense and T1-hypointense lesion volumes, normalized brain volume and average lesion MT ratio (MTR) were measured. MTR histograms from the whole brain tissue were also obtained. Clinical multiple sclerosis evolution and neurological disability were re-assessed in all patients after a median follow-up of 4.5 years. A multivariate analysis was performed to establish which clinical and MRI-derived variables were significant predictors of neurological deterioration at the end of the study period. At the end of follow-up, 34 patients showed significant neurological deterioration. The final multivariable model included average brain MTR percentage change after one year [P = 0.02, odds ratio (OR) = 0.86] and baseline T2-hyperintense lesion volume (P = 0.04, OR=1.04) as independent predictors of medium-term disability accumulation (r2 = 0.23). In this cohort of patients, abnormal values of average brain MTR changes showed a relatively high specificity (76.9%) and positive predictive value (59.1%) for Expanded Disability Status Scale score deterioration in individual cases. In patients with multiple sclerosis, a comprehensive estimation of the short-term changes of both conventional and MT MRI-detectable lesion burden might provide useful prognostic information for the medium-term clinical disease evolution.

Adult↗

PubMedDate not supplied

Temporal evolution and prognostic significance of postoperative spikes after selective amygdala-hippocampectomy.

The purpose of this study was to quantify the temporal evolution and to determine the prognostic significance of spikes on serial postoperative EEGs after selective amygdala-hippocampectomy. The authors performed postoperative EEGs 4 months, 1 year, and 2 years after surgery in 31 patients with unilateral mesial temporal lobe epilepsy. Spike frequency was determined ipsilateral to the resection (group I, no spikes; group II, 1 to 10 spikes; group III, 11 to 20 spikes; group IV, more than 21 spikes during the 30-minute recording). The temporal evolution of postoperative spike frequency was assessed, and these parameters were correlated with surgical outcome. Twenty-two patients showed spikes on postoperative EEG. Spike frequency decreased over time in 14 patients, while no changes or minimal changes occurred in seven patients, and spike frequency increased in one patient. Nine patients had no spikes. There was no correlation between occurrence, frequency, and temporal evolution of spikes with postoperative seizure control. The authors' results demonstrate a progressive decrease of spike frequency during the postoperative period after selective amygdala-hippocampectomy, although occurrence, frequency, and temporal evolution of postoperative spikes had no implications on surgical outcome.

Adult↗

PubMedDate not supplied

Clonal evolution as the limiting factor in the detection of minimal residual disease by polymerase chain reaction in children in Brazil with acute lymphoid leukemia.

BACKGROUND: The purpose of this investigation was to analyze the incidence of clonal evolution in children in Brazil children with acute lymphoblastic leukemia and its interference with the detection of minimal residual disease by polymerase chain reaction using clone-specific primers. PATIENTS AND METHODS: The authors analyzed DNA samples from 12 children with acute lymphoblastic leukemia at diagnosis and after relapse using polymerase chain reaction and automatic sequencing to determine the presence of T-cell receptor gamma (TCRgamma) gene rearrangements. A clone-specific primer was synthesized based on the sequence obtained at diagnosis for each patient and at relapse for those with clonal evolution for the study of minimal residual disease. RESULTS: A change of the original clone was detected in 3 of 12 patients (25%), involving the same rearrangement detected at diagnosis, suggesting the development of subclones. Minimal residual disease was detected at the end of treatment or before the relapse in all patients who had maintained the same rearrangements detected at diagnosis. Minimal residual disease was investigated at the end of treatment in two of the three patients with clonal evolution and was not detected with the use of clone-specific primers. CONCLUSIONS: These data suggest that clonal evolution for TCRgamma gene rearrangements was not a rare event among children in Brazil and, when present, interfered with the detection of minimal residual disease.

Acute Disease↗

PubMed2006

The evolution of spinal instrumentation for the management of occipital cervical and cervicothoracic junctional injuries.

STUDY DESIGN/SETTING: Independent computer-based literature review of articles pertaining to instrumentation and fusion of junctional injuries of the cervical spine. OBJECTIVE: To review and discuss the evolution of instrumentation techniques and systems used in the treatment of cervical spine junctional injuries. SUMMARY OF BACKGROUND DATA: Instrumentation of junctional injuries of the cervical spine has been limited historically by failure to achieve rigid internal fixation in multiple planes. The evolution of these techniques has required increased insight into the morphology and unique biomechanics of the structures to be instrumented. METHODS: Computer-based literature search of Ovid and PubMed databases. RESULTS: Extensive literature search yielded insights into the evolution of systems initially based on onlay bone graft combined with wiring techniques. Such techniques have come to include systems incorporating rigid, longitudinal struts that accommodate multiplanar screws placed in the lateral masses, pedicles, transarticular regions, and occipital bone. CONCLUSIONS: Despite a rapid evolution of techniques and instrumentation technologies, it remains incumbent on the physician to provide the patient with a surgical procedure that balances the likelihood of a favorable outcome with the risk inherent in the implementation of the procedure.

Cervical Vertebrae↗

PubMed2004

Different evolutions in heart rate variability after heart transplantation: 10-year follow-up.

BACKGROUND: After heart transplantation, the donor heart is extrinsically denervated. No input of sympathetic or vagal nerves can influence the heart rate, resulting in a flat power spectrum of the beat-to-beat variability. The occurrence and the significance of reinnervation remain controversial. METHODS AND RESULTS: We monitored the evolution of heart rate variability (HRV) after heart transplantation, starting from a few weeks postoperatively up to 10 years after surgery. Twenty-four-hour Holter recordings of 216 heart-transplant patients were analyzed using time and frequency domain analysis of HRV. Analysis of all data revealed an increase in 24-hour and night-time total power starting from 2 years after transplantation. Low-frequency oscillations calculated over the total 24 hours, day- and nighttime increased significantly starting from year 4 and onward (year 4-8: P < 0.005). No evolution was found in high-frequency power. Subgroup analysis revealed a group with a clear spectral component (n = 16), a group with a small component (n = 124), and a group with a flat spectrum (n = 76). Only the first group revealed an evolution in both high- and low-frequency power. CONCLUSION: These results indicate three different types of evolution in HRV, with reinnervating patterns present in only a minority of the patients. The vast majority of the patients show no signs of reinnervation.

Blood Pressure↗

PubMed1980

Experiments in microbial evolution: new enzymes, new metabolic activities.

Biological evolution has resulted in a richness and diversity of species. Among microorganisms this is most evident in the wealth and diversity of biochemical transformations. Evidence for evolutionary relationships may be obtained from comparative studies, but with microorganisms it is also possible to follow evolution in action. Microbial populations adapt rapidly to changes in the environment and the evolution of new metabolic activities can be observed in laboratory experiments. The enzymes of many catabolic pathways are synthesized in response to the presence of inducing substrates. New catabolic activities may be acquired by mutations in regulatory genes resulting in alterations in the specificity of induction, or in enzyme synthesis in the absence of inducer. Mutations in structural genes may given rise to enzymes with altered substrate specificities. In bacteria, catabolic genes may be carried on plasmids and the exchange of plasmids among bacterial populations increases the evolutionary potential. Experiments in microbial evolution have produced strains with novel catabolic activities involving regulatory or structural gene mutations, gene duplications and plasmid exchange. Enzymes studied in this way include amidase, ribitol dehydrogenase, evolved beta-galactosidase, and enzymes of the catabolic pathways for pentoses and pentitols and haloaromatic compounds.

Amidohydrolases↗

PubMed2003

Dollo's law and the re-evolution of shell coiling.

Gastropods have lost the quintessential snail feature, the coiled shell, numerous times in evolution. In many cases these animals have developed a limpet morphology with a cap-shaped shell and a large foot. Limpets thrive in marginal habitats such as hydrothermal vents, the high-energy rocky intertidal areas and fresh water, but they are considered to be evolutionary dead-ends, unable to re-evolve a coiled shell and therefore unable to give rise to the diversity seen among coiled snails. The re-evolution of a coiled shell, or any complex character, is considered unlikely or impossible (Dollo's law) because the loss of the character is followed by the loss of the genetic architecture and developmental mechanisms that underlie that character. Here, we quantify the level of coiling in calyptraeids, a family of mostly uncoiled limpets, and show that coiled shells have re-evolved at least once within this family. These results are the first demonstration, to our knowledge, of the re-evolution of coiling in a gastropod, and show that the developmental features underlying coiling have not been lost during 20-100 Myr of uncoiled evolutionary history. This is the first example of the re-evolution of a complex character via a change in developmental timing (heterochrony) rather than a change in location of gene expression (heterotopy).

Adaptation, Biological↗

PubMed2003

Evolution of photosensory pineal organs in new light: the fate of neuroendocrine photoreceptors.

Pineal evolution is envisaged as a gradual transformation of pinealocytes (a gradual regression of pinealocyte sensory capacity within a particular cell line), the so-called sensory cell line of the pineal organ. In most non-mammals the pineal organ is a directly photosensory organ, while the pineal organ of mammals (epiphysis cerebri) is a non-sensory neuroendocrine organ under photoperiod control. The phylogenetic transformation of the pineal organ is reflected in the morphology and physiology of the main parenchymal cell type, the pinealocyte. In anamniotes, pinealocytes with retinal cone photoreceptor-like characteristics predominate, whereas in sauropsids so-called rudimentary photoreceptors predominate. These have well-developed secretory characteristics, and have been interpreted as intermediaries between the anamniote pineal photoreceptors and the mammalian non-sensory pinealocytes. We have re-examined the original studies on which the gradual transformation hypothesis of pineal evolution is based, and found that the evidence for this model of pineal evolution is ambiguous. In the light of recent advances in the understanding of neural development mechanisms, we propose a new hypothesis of pineal evolution, in which the old notion 'gradual regression within the sensory cell line' should be replaced with 'changes in fate restriction within the neural lineage of the pineal field'.

Animals↗

PubMed2006

Averaged time evolution of rough surfaces.

We propose a method of extracting an approximated evolution equation of distribution of height fluctuations for a class of discrete growth models of rough surfaces where the behavior of local slopes can be described by a Markov process. Using the Markov property of the fluctuating field, the evolution equation is obtained as a map describing the time evolution averaged over possible growth paths. Applying the method to a -dimensional restricted solid-on-solid model, we obtain a map with finite degrees of freedom. The obtained map describes well the averaged evolution of surfaces.

Journal Article↗

PubMed2006

Evolution of light-induced anchoring in dye-doped nematics: experiment and model.

A series of experiments was carried out to describe the evolution of light-induced anchoring in dye-doped nematic liquid crystals (LCs) at irradiation with polarized light. The experiments included cells filled with a pure pentyl-cyanobiphenyl (5CB) and containing a layer of azo dye deposited on an aligning film, as well as cells filled with azo dye doped 5CB, which allowed us to distinguish the role of "surface" and "bulk" dye molecules in the evolution of light-induced anchoring. Modifications of the spectra of spontaneously adsorbed dye molecules under illumination enabled us to assert that light-induced desorption is a mechanism responsible for producing an easy orientation axis in a dark-adsorbed layer. We found that the evolution of light-induced anchoring involves a competition between light-induced desorption and adsorption of the dye molecules on the aligning surface, and the final anchoring is determined by the total light irradiation dose. These data allowed introducing a theoretical model of light-induced anchoring of dye-doped nematic LCs that quantitatively described the experimental results and portrayed the whole evolution of the dye-doped LC cell at irradiation.

Journal Article↗

PubMed2004

Energy dependence of the Cronin effect from nonlinear QCD evolution.

The nonlinear evolution of dense partonic systems has been suggested as a novel physics mechanism relevant for the dynamics of p-A and A-A collisions at collider energies. Here we study to what extent the description of Cronin enhancement in the framework of this nonlinear evolution is consistent with the recent observation in sqrt[s]=200 GeV d-Au collisions at the Relativistic Heavy Ion Collider. We solve the Balitsky-Kovchegov evolution equation numerically for several initial conditions encoding Cronin enhancement. We find that the properly normalized nuclear gluon distribution is suppressed at all momenta relative to that of a single nucleon. For the resulting spectrum of produced gluons in p-A and A-A collisions, the nonlinear QCD evolution is unable to generate a Cronin-type enhancement, and it quickly erases any such enhancement which may be present at lower energies.

Journal Article↗