John Baldwin

Bio: John Baldwin is an academic researcher from University of British Columbia. The author has contributed to research in topics: Breakwater & Wind wave. The author has an hindex of 8, co-authored 15 publications receiving 538 citations. Previous affiliations of John Baldwin include Monash University, Clayton campus.

Functional significance of isoenzymes in thermal acclimatization. Acetylcholinesterase from trout brain

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.

Wave interactions with double slotted barriers

Abstract: The present article outlines the numerical calculation of wave interactions with a pair of thin vertical slotted barriers extending from the water surface to some distance above the seabed, and describes laboratory tests undertaken to assess the numerical model. The numerical model is based on an eigenfunction expansion method and utilizes a boundary condition at the surface of each barrier which accounts for energy dissipation within the barrier. Comparisons with experimental measurements of the transmission, reflection, and energy dissipation coefficients for partially submerged slotted barriers show excellent agreement and indicate that the numerical method is able to adequately account for the energy dissipation by the barriers.

Wave Interactions with Perforated Breakwater

Abstract: The present paper describes a theoretical analysis and an associated numerical model used to assess the performance of a breakwater consisting of a perforated front wall, an impermeable back wall, and a rock-filled core. The numerical method is based on an eigenfunction expansion and utilizes a boundary condition at the perforated wall that accounts for energy dissipation. The numerical model is validated by comparison with previous numerical studies of the limiting cases of a permeable seawall and a perforated breakwater with an impermeable back wall. Relevant numerical results that are presented relate to the reflection coefficient, the wave runup, and the wave force. The effects of porosity, breakwater geometry, and relative wavelength are discussed; the choice of suitable parameters needed to model the permeability of the breakwater is described; and an example application to a practical design situation is given.

Natural Modes of Modified Structures

Abstract: Nomenclature C = matrix of admixture coefficients for mode shape changes / = identity matrix K = symmetric stiffness matrix . £_ = modification vector M = symmetric mass matrix u = modification vector in modal coordinates x — displacement vector z = displacement vector in modal coordinates a. = magnitude of local stiffness modification A = change between baseline and modified structures X = natural frequency of modified structure $ = modal matrix with columns k k = kih mode shape vector i = Ath mode shape vector of modified structure ft = frequency matrix with diagonals co oo = natural frequency of baseline structure

Wave Propagation Past a Pile-Restrained Floating Breakwater

Abstract: The present paper describes a numerical and experimental study of wave propagation past a pile-restrained floating breakwater. The numerical model is based on two-dimensional wave diffraction theory for wave interaction with a long horizontal cylinder and is applied to the common case of a rectangular-section breakwater subjected to normally incident waves. Comparisons with experimental measurements show excellent agreement and the effect of a gap between the piles and the breakwater is discussed. Relevant results for the wave transmission and heave motion of the breakwater in deep water are presented as functions of the relative wave frequency for various beam to draft ratios. *ISOPE Member. Received March 23, 1998: revised manuscript received by the editors September 15, 1998. The original version was submitted directly to the Journal.

Cold-adapted enzymes.

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...

Living in the Now: Physiological Mechanisms to Tolerate a Rapidly Changing Environment

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.

Some like it cold: biocatalysis at low temperatures.

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.

Adaptation of enzymes to temperature: searching for basic "strategies".

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.

Temperature Adaptation of Enzymes: Biological Optimization Through Structure-Function Compromises

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-