Functional significance of isoenzymes in thermal acclimatization. Acetylcholinesterase from trout brain
TL;DR: It is concluded that the K(m)-temperature relationship is adaptive, and that the critical process during thermal acclimatization, in cases where enzymes show sharp changes in K( m) with temperature, is the synthesis of a new enzyme variant that is better suited for catalysis and control of catalysis under the conditions of theacclimatized state.
Abstract: 1. The effects of acclimatization temperature on the catalytic properties of acetylcholinesterase from rainbow-trout brain were examined. 2. Trout brain acetylcholinesterase occurs in two distinct forms. A single ;warm' variant of the enzyme is present after acclimatization to 17 degrees C; a single ;cold' variant appears after acclimatization to 2 degrees C. Both forms are present in fish after acclimatization to an intermediate temperature. 3. The K(m) values of the enzyme variants for acetylcholine are temperature-dependent, the lowest values coinciding with the acclimatization temperature at which each enzyme was induced. 4. It is concluded that the K(m)-temperature relationship is adaptive, and that the critical process during thermal acclimatization, in cases where enzymes show sharp changes in K(m) with temperature, is the synthesis of a new enzyme variant that is better suited for catalysis and control of catalysis under the conditions of the acclimatized state.
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TL;DR: This review addresses the structure, function, and stability of cold-adapted enzymes, highlighting the challenges for immediate and future consideration.
Abstract: By far the largest proportion of the Earth's biosphere is comprised of organisms that thrive in cold environments (psychrophiles). Their ability to proliferate in the cold is predicated on a capacity to synthesize cold-adapted enzymes. These enzymes have evolved a range of structural features that confer a high level of flexibility compared to thermostable homologs. High flexibility, particularly around the active site, is translated into low-activation enthalpy, low-substrate affinity, and high specific activity at low temperatures. High flexibility is also accompanied by a trade-off in stability, resulting in heat lability and, in the few cases studied, cold lability. This review addresses the structure, function, and stability of cold-adapted enzymes, highlighting the challenges for immediate and future consideration. Because of the unique properties of cold-adapted enzymes, they are not only an important focus in extremophile biology, but also represent a valuable model for fundamental researc...
749 citations
TL;DR: In this review, examples of mechanisms, focusing on those underlying physiological plasticity, that operate in contemporary organisms as a means to consider physiological responses that are available to organisms in the future are highlighted.
Abstract: Rising atmospheric carbon dioxide has resulted in scientific projections of changes in global temperatures, climate in general, and surface seawater chemistry. Although the consequences to ecosystems and communities of metazoans are only beginning to be revealed, a key to forecasting expected changes in animal communities is an understanding of species' vulnerability to a changing environment. For example, environmental stressors may affect a particular species by driving that organism outside a tolerance window, by altering the costs of metabolic processes under the new conditions, or by changing patterns of development and reproduction. Implicit in all these examples is the foundational understanding of physiological mechanisms and how a particular environmental driver (e.g., temperature and ocean acidification) will be transduced through the animal to alter tolerances and performance. In this review, we highlight examples of mechanisms, focusing on those underlying physiological plasticity, that operate in contemporary organisms as a means to consider physiological responses that are available to organisms in the future.
549 citations
Cites background from "Functional significance of isoenzym..."
...However, in addition to changing protein concentration, thermal acclimation in some cases can change the isoform of a specific protein that is expressed such that organisms can “switch” isoforms to one that better suited to a particular thermal environment (25)....
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TL;DR: The emerging picture suggests that psychrophilic enzymes are characterized by an improved flexibility of the structural components involved in the catalytic cycle, whereas other protein regions, if not implicated in catalysis, may be even more rigid than their mesophilic counterparts.
Abstract: In the last few years, increased attention has been focused on a class of organisms called psychrophiles. These organisms, hosts of permanently cold habitats, often display metabolic fluxes more or less comparable to those exhibited by mesophilic organisms at moderate temperatures. Psychrophiles have evolved by producing, among other peculiarities, “cold-adapted” enzymes which have the properties to cope with the reduction of chemical reaction rates induced by low temperatures. Thermal compensation in these enzymes is reached, in most cases, through a high catalytic efficiency associated, however, with a low thermal stability. Thanks to recent advances provided by X-ray crystallography, structure modelling, protein engineering and biophysical studies, the adaptation strategies are beginning to be understood. The emerging picture suggests that psychrophilic enzymes are characterized by an improved flexibility of the structural components involved in the catalytic cycle, whereas other protein regions, if not implicated in catalysis, may be even more rigid than their mesophilic counterparts. Due to their attractive properties, i.e., a high specific activity and a low thermal stability, these enzymes constitute a tremendous potential for fundamental research and biotechnological applications.
398 citations
Cites background from "Functional significance of isoenzym..."
...This process is particularly useful for seasonal reversible adaptation mechanisms, as observed in fish [39] and nematode enzymes [40]....
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TL;DR: These studies, begun in Peter Hochachka's laboratory almost 40 years ago, have been instrumental in the development of a conceptual framework for the study of biochemical adaptation, a field whose origin can be traced largely to his creative influences.
Abstract: The pervasive influence of temperature on biological systems necessitates a suite of temperature--compensatory adaptations that span all levels of biological organization--from behavior to fine-scale molecular structure. Beginning about 50 years ago, physiological studies conducted with whole organisms or isolated tissues, by such pioneers of comparative thermal physiology as V.Ya. Alexandrov, T.H. Bullock, F.E.J. Fry, H. Precht, C.L. Prosser, and P.F. Scholander, began to document in detail the abilities of ectothermic animals to sustain relatively similar rates of metabolic activity at widely different temperatures of adaptation or acclimation. These studies naturally led to investigation of the roles played by enzymatic proteins in metabolic temperature compensation. Peter Hochachka's laboratory became an epicenter of this new focus in comparative physiology. The studies of the enzyme lactate dehydrogenase (LDH) that he initiated as a PhD student at Duke University in the mid-1960s and continued for several years at the University of British Columbia laid much of the foundation for subsequent studies of protein adaptation to temperature. Studies of orthologs of LDH have revealed the importance of conserving kinetic properties (catalytic rate constants (kcat) and Michaelis-Menten constants (Km) and structural stability during adaptation to temperature, and recently have identified the types of amino acid substitutions causing this adaptive variation. The roles of pH and low-molecular-mass organic solutes (osmolytes) in conserving the functional and structural properties of enzymes also have been elucidated using LDH. These studies, begun in Peter Hochachka's laboratory almost 40 years ago, have been instrumental in the development of a conceptual framework for the study of biochemical adaptation, a field whose origin can be traced largely to his creative influences. This framework emphasizes the complementary roles of three "strategies" of adaptation: (1) changes in amino acid sequence that cause adaptive variation in the kinetic properties and stabilities of proteins, (2) shifts in concentrations of proteins, which are mediated through changes in gene expression and protein turnover; and (3) changes in the milieu in which proteins function, which conserve the intrinsic properties of proteins established by their primary structure and modulate protein activity in response to physiological needs. This theoretical framework has helped guide research in adaptational biochemistry for many years and now stands poised to play a critical role in the post-genomic era, as physiologists grapple with the challenge of integrating the wealth of new data on gene sequences (genome), gene expression (transcriptome and proteome), and metabolic profiles (metabolome) into a realistic physiological context that takes into account the evolutionary histories and environmental relationships of species.
315 citations
Cites background from "Functional significance of isoenzym..."
...Thus, although adaptation of enzymes to temperature continued to be examined in his laboratory for a few more years, notably by his two students John Baldwin (Baldwin and Hochachka, 1969; Baldwin, 1971) and Tom Moon (Moon and Hochachka, 1971), the transition to an emphasis on adaptations to oxygen was well underway....
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...…adaptation of enzymes to temperature continued to be examined in his laboratory for a few more years, notably by his two students John Baldwin (Baldwin and Hochachka, 1969; Baldwin, 1971) and Tom Moon (Moon and Hochachka, 1971), the transition to an emphasis on adaptations to oxygen was well…...
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TL;DR: Most aspects of enzyme structure and function are highly sensitive to temperature variation, whether this variation occurs rapidly or over long evolutionary time, and the so-called "goals" of temperature adaptation are identified.
Abstract: The effects of temperature on enzyme structure and function have long been of interest to comparative physiologists and biochemists, and the findings of the past ten years have shown convincingly that temperature stresses on enzymes, and the adaptive responses of enzymes to compensate for these stresses, have played an important role in biological evolution. Many aspects of enzymatic adaptation to temperature have been treated thoroughly in recent monographs (3) and reviews (48, 56, 104), and these sources provide extensive bibliographies of the hundreds of papers dealing with temperature-enzyme interactions. This review attempts to com plement existing reviews and to provide an overview of the important structure function interrelationships that characterize enzymatic adaptation to temperature. This review also attempts to show how the effects of temperature on enzyme struc ture and function may be instrumental in establishing the thermal optima and tolerance limits of metabolic function and, thereby, of the organism itself. Hope fully, this discussion will help to provide a bridge between the interesting new discoveries of enzyme chemists and interests of ecologists, systematists, and zoo geographers. Attention is first directed toward the sources of thermal stress on enzyme systems; this analysis reveals that most aspects of enzyme structure and function are highly sensitive to temperature variation, whether this variation occurs rapidly or over long evolutionary time. Next the so-called "goals" of temperature adaptation are qut lined, namely the set of properties that must be conserved in all organisms, under all thermal regimes. The molecular mechanisms instrumental in effecting these critical conservative adaptations are then discussed. Several distinct classes of mech-
293 citations
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Journal Article•
TL;DR: Procedures are described for measuring protein in solution or after precipitation with acids or other agents, and for the determination of as little as 0.2 gamma of protein.
289,852 citations
TL;DR: The technique of disc electrophoresis has been presented, including a discussion of the technical variables with special reference to the separation of protein fractions of normal human serum.
Abstract: Summary
The technique of disc electrophoresis has been presented, including a discussion of the technical variables with special reference to the separation of protein fractions of normal human serum.
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283 citations
TL;DR: It is suggested that the numerous examples in the literature of anomalous Arrhenius plots may be due to thermally induced reversible changes in protein structure.
236 citations
TL;DR: The results suggest that in evolutionary adaptation to temperature, enzyme affinity for substrate is a feature more sensitive to natural selection than is molecular activity per se.
213 citations