Serine hydroxymethyltransferase: origin of substrate specificity.

All forms of serine hydroxymethyltransferase, for which a primary structure is known, have five threonine residues near the active-site lysyl residue (K229) that forms the internal aldimine with pyridoxal phosphate. For Escherichia coli serine hydroxymethyltransferase each of these threonine residues has been changed to an alanine residue. The resulting five mutant enzymes were purified and characterized with respect to kinetic and spectral properties. The mutant enzymes T224A and T227A showed no significant changes in kinetic and spectral properties compared to the wild-type enzyme. The T225A and T230A enzymes exhibited differences in Km and kcat values but exhibited the same spectral properties as the wild-type enzyme. The four threonine residues at positions 224, 225, 227, and 230 do not play a critical role in the mechanism of the enzyme. The T226A enzyme had nearly normal affinity for substrates and coenzymes but had only 3% of the catalytic activity of the wild-type enzyme. The spectrum of the T226A enzyme in the presence of amino acid substrates showed a large absorption maximum at 343 nm with only a small absorption band at 425 nm, unlike the wild-type enzyme whose enzyme-substrate complexes absorb at 425 nm. Rapid reaction studies showed that when amino acid substrates and substrate analogues were added to the T226A enzyme, the internal aldimine absorbing at 422 nm was rapidly converted to a complex absorbing at 343 nm in a second-order process. This was followed by a very slow first-order formation of a complex absorbing at 425 nm.(ABSTRACT TRUNCATED AT 250 WORDS)     

Functional evolution: origin and problems

In the article the history of comparative and evolutionary physiology since the early XIX is given. The most substantial methods of evolutionary physiology are described. In the mid-50ies Orbely put forward the suggestion concerning two tasks facing evolutionary physiology, namely the study of evolution of functions and functional evolution. In the present work attention is given to the principles underlying evolution of functions on different levels of physiological systems. The main aspects of functional evolution are discussed.     

Leishmania: origin, evolution and future since the Precambrian

This brief review discusses the history of leishmaniasis, considering its origin from the Paleoartic, Neoartic or Neotropic. We reassess some of the theories of the likely origin of this protozoan since the beginning of life on Earth, passing through the Mesozoic and continuing to the appearance of humans. The relationship between this parasite or its ancestors, possible vectors and hosts with regard to ecological modifications is discussed. Recent molecular techniques have helped to elucidate some of the evolutionary questions regarding Leishmania, but have also brought doubts about the origin and evolution of this human parasite. PCR has been used for studies in the new discipline of paleoparasitology, helping to elucidate some of the remaining evolutionary questions. Understanding of this global condition is fundamental in determining the best approach to use against the parasite, specifically for the development of an efficient vaccine.     

Livestock-associated Staphylococcus aureus: origin, evolution and public health threat

Staphylococcus aureus is a major pathogen responsible for severe nosocomial and community-associated infections of humans and infections of economically important livestock species. In recent years, studies into livestock-associated S. aureus including methicillin-resistant (MRSA) strains have provided new information regarding their origin and host adaptation, and their capacity to cause zoonotic infections of humans. Furthermore, a potential role for human activities such as domestication and industrialisation in the emergence of S. aureus clones affecting livestock has been highlighted. Here, I summarise recent developments in this emerging field and suggest questions of importance for future research efforts.     

Mechanism, origin, and evolution of anoxia tolerance in animals

Organisms vary widely in their tolerance to conditions of limiting oxygen supply to their cells and tissues. A unifying framework of hypoxia tolerance is now available that is based on information from cell-level models from highly anoxia-tolerant species, such as the aquatic turtle, and from other more hypoxia-sensitive systems. The response of hypoxia-tolerant systems to oxygen lack occurs in two (defense and rescue) phases. The first lines of defense against hypoxia include a drastic, if balanced, suppression of ATP demand and supply pathways; this regulation allows ATP levels to remain constant, even while ATP turnover rates greatly decline. The ATP requirements of ion pumping are down-regulated by generalized ‘channel’ arrest in hepatocytes and by the arrest of specific ion channels in neurons. In hepatocytes, the ATP demands of protein synthesis are down-regulated on exposure to hypoxia by an immediate global blockade of the process (probably through translational arrest caused by complexing between polysomes and elongation factors). In hypoxia-sensitive cells, this translational arrest seems irreversible, but hypoxia-tolerant systems activate ‘rescue’ mechanisms if the period of oxygen lack is extended by preferentially regulating the expression of several proteins. In these cells, a cascade of processes underpinning hypoxia rescue and defense begins with an oxygen sensor (a heme protein) and a signal transduction pathway that leads to the specific activation of some genes (increased expression of several proteins) and to specific down-regulation of other genes (decreased expression of several other proteins). The functional roles of the oxygen-sensing and signal-transduction system include significant gene-based metabolic reprogramming — the rescue process — with maintained down-regulation of energy demand and supply pathways in metabolism throughout the hypoxic period. We consider that, through this recent work, it is becoming evident how normoxic-maintenance ATP turnover rates can be down-regulated by an order of magnitude or more — to a new hypometabolic steady state, which is prerequisite for surviving prolonged hypoxia or anoxia. Because the phylogenies of the turtles and of fishes are well known, we are now in an excellent position to assess conservative vs. adaptable features in the evolution of the above hypoxia-response physiology in these two specific animal lineages.     

Human drowning: Phylogenetic origin

Because most animals are able to survive much longer when in water than most humans and apes, it is likely that at some time during human phylogeny the-innate-ability to swim like animals has been lost. Paleontology and comparative zoology provide indications for selective pressures and adaptations explaining this phenomenon. Among these are (a) buoyancy having become reduced slightly due to a smaller lung air/body weight ratio, less air trapped in the body covering hairs and reduction in gastrointestinal gas, (b) the caudally directed nasal entrance cranially to which there is the heavy neurocranium, (c) the low position of the laryngeal entrance, (d) the ineffective propulsion by the human innate crawling and walking movements, and (e) the well developed cerebrum being present cranially to the airway entrance, being sensitive for anoxia and hypothermia, and causing behaviour adding to drowning risks.     

Life forms of Pteridophyta, their origin and evolution

The following separation of the main growth forms of Pteridophyta is proposed: thin-rhizomatous, creeping-rosetted, ascending-rosetted, vertical-rosetted, and arborescent. Each of these can be divided into life forms according to a series of morphological and other characters. The most primitive growth form of Pteridophyta is acknowledged as the thin-rhizomatous. In the course of evolution toward polymerization and integration of fronds, the group of arborescent Pteridophyta were transformed into shoot plants, initially of the Cycas type. Water ferns (Salviniaceae) and seed ferns (Pteridospermae) are known as the arbitrary type of Lycopsida which did not reach the state of shot structure of the body. In this respect, Equisetales occupy an intermediate position. It may be assumed that in the evolution of plants, the change in their life forms was of paramount significance.     

The origin,patterning and evolution of insect appendages

The appendages of the adult fruit fly and other insects and Arthropods develop from secondary embryonic fields that form after the primary anterior/posterior and dorsal/ventral axes of the embryo have been determined. In Drosophila, the position and fate of the different fields formed within each segment are determined by genes acting along both embryonic axes, within individual segments, and within specific fields. Since the major architectural differences between most Arthropod classes and orders involve variations in the number, type and morphology of body appendages, the elucidation of the embryology and molecular genetics of the origin and patterning of insect limb fields may help to facilitate an understanding of both the mechanism of appendage formation and some of the major steps in the morphological evolution of the Arthropods. In this review, we will discuss recent studies that have advanced our understanding of both the origin and patterning of Drosophila leg and wing secondary fields. These results provide fresh insights into potentially general mechanisms of how body parts develop and evolve.     

Mosaic evolution in the origin of the Hominoidea.

The initial appearance of hominoids, or apes, and the selective pressures that led to their emergence are currently disputed. Central to the argument are the proconsulids, variously described as the earliest apes or as stem catarrhines, based on facial and postcranial data, respectively. The present paper reports on incongruence and parsimony analyses applied to a combined data set. The results demonstrate that proconsulids are cladistic hominoids, and that the apparent incongruence between the data sets is due to mosaic evolution; the earliest changes in Hominoidea occurred in the face. These results suggest that the initial divergence of hominoids involved selection for an ape-like face, and was not driven by an adaptive shift to below-branch locomotion.