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A F Bennett

Publications and source records attributed to A F Bennett.

16 recordsLinked to original sources
PubMed1992

Bundling of microtubules by synapsin 1. Characterization of bundling and interaction of distinct sites in synapsin 1 head and tail domains with different sites in tubulin.

Synapsin 1 is a nerve terminal phosphoprotein whose role seems to encompass the linking of small synaptic vesicles to the cytoskeleton. Synapsin 1 can join small synaptic vesicles to neuronal spectrin, microfilaments and microtubules; it can also bundle microtubules and microfilaments. In this paper, the mode of interaction between synapsin 1 and microtubules has been investigated. Bundling is shown to be highly cooperative: the apparent Hill coefficient is 3.06 +/- 0.3, and bundling is half-maximal at 0.63 +/- 0.02 microM. Bundling occurs either when whole synapsin 1 preparations (containing monomers and oligomers) or when monomeric synapsin 1 is added to microtubules. However, it is not clear that synapsin 1 remains monomeric in the presence of microtubules. Synapsin 1-microtubule mixtures contain two types of filament. One type is characterised by microtubules often with synapsin 1 bound to their surface. The other type is composed of filaments of diameter 15 +/- 5 nm. This filament type is granular and made up in part of 14-nm-diameter particles. These dimensions are consistent with their being made up of polymerised synapsin 1. It is possible that microtubules induce the polymerisation of synapsin 1. Synapsin 1 had independent tubulin binding sites in the N-terminal head domain and in the C-terminal tail domain. Whole synapsin 1 can interact with tubulin after it has been digested to remove the tubulin C terminus (des-C-terminal tubulin). The interaction of des-C-terminal tubulin with synapsin 1 appears to be via the head domain, since 125I-des-C-terminal tubulin only shows specific binding to the head domain on gel blots. By contrast intact tubulin binds to both head and tail domains. Binding to the tail domain can be inhibited by a synthetic peptide representing the microtubule-associated protein 2 (MAP2) binding site of class II beta tubulin. These results suggest a model for microtubule bundling by synapsin 1 in which independent sites in the head and tail domains of synapsin 1 cross-link microtubules by interactions with two distinct sites in tubulin.

Animals↗
PubMed1991

Site specificity in the interactions of synapsin 1 with tubulin.

Synapsin 1 is one of a family of phosphoproteins located on small synaptic vesicles (SSV) in the presynaptic terminal, and probably plays a critical role in the process of neuronal exocytosis by providing regulated linkages between SSV and the cytoskeleton. Two forms of synapsin 1 are produced from a single gene by differential mRNA splicing: 1a, 706 amino acid residues, and 1b, 670 residues. Synapsin 1 has two structural domains, a globular N-terminal head domain and an elongated tail domain. Electron microscopy of nerve terminals in situ and reconstitution studies in vitro indicates that synapsin 1 can interact with microtubules, microfilaments and brain spectrin. In vitro, synapsin 1 can bundle microtubules. This could either occur by synapsin 1 being at least bivalent for microtubules, or by univalent synapsin 1 molecules aggregating to form complexes that are more than univalent. To resolve this question, we have taken the approach of preparing defined fragments of synapsin 1 from each structural domain and analysing them for tubulin-binding activity. Our results show that there are tubulin-binding sites in both head and tail domains. We conclude that synapsin 1 monomers should be able to cross-link microtubules.

Amino Acid Sequence↗
PubMed1991

Selective Ca2(+)-dependent interaction of calmodulin with the head domain of synapsin 1.

The calcium-dependent regulatory protein calmodulin is a critical element in the machinery regulating exocytosis at nerve terminals. Okabe & Sobue [(1987) FEBS Lett. 213, 184-188] showed that calmodulin interacts with one of the proteins intimately connected with the neuronal exocytotic process, i.e. synapsin 1. We have investigated the site at which calmodulin interacts with synapsin 1. We find that it is possible to generate chemically cross-linked Ca2(+)-dependent complexes between synapsin 1 and calmodulin in vitro, and have used covalent cross-linking in conjunction with calmodulin affinity chromatography to identify fragments of synapsin 1 that interact with calmodulin. Ca2(+)-dependent calmodulin binding is restricted to the 'head' domain (residues 1-453 in bovine synapsin 1). Within this domain the binding site is located in a unique 11 kDa Staphylococcus aureus V8 proteinase generated fragment. This fragment does not contain the site for cyclic-AMP-dependent phosphorylation and therefore does not represent the N-terminus of the protein.

Animals↗
PubMed1991

The evolution of activity capacity.

The capacities of animals for activity (burst speed, maximal exertion, endurance) are examined in relation to their selective importance in extant populations and the pattern of their evolution in major animal taxa. Activity capacities have been demonstrated to be both heritable and highly variable in natural populations and hence susceptible to natural selection. Some field studies have demonstrated significant positive associations between activity capacities, particularly burst speed, and survivorship; other studies have not. The potential for such selection therefore clearly exists, although it may not operate in all populations. Comparative studies of major taxa have linked endurance capacities to maximal rates of oxygen consumption; speed and exertion are correlated with capacities for anaerobic metabolism, either the catabolism of phosphagens or the production of lactic acid or octopine, depending on taxon. In vertebrates, the primitive metabolic pattern involved the use of aerobic metabolism to support moderate swimming performance, supplemented by bursts of activity fuelled through lactic acid production. Because of much greater locomotor costs, the transition of vertebrates onto land entailed a decrease in endurance, which was greatly expanded again only after the evolution of the higher rates of aerobic metabolism characteristic of the birds and mammals. These greater aerobic capacities may have been selected for thermoregulatory reasons and/or for increased activity capacity itself.

Animals↗
PubMed1990

Rapid evolution in response to high-temperature selection.

Temperature is an important environmental factor affecting all organisms, and there is ample evidence from comparative physiology that species and even conspecific populations can adapt genetically to different temperature regimes. But the effect of these adaptations on fitness and the rapidity of their evolution is unknown, as is the extent to which they depend on pre-existing genetic variation rather than new mutations. We have begun a study of the evolutionary adaptation of Escherichia coli to different temperature regimes, taking advantage of the large population sizes and short generation times in experiments on this bacterial species. We report significant improvement in temperature-specific fitness of lines maintained at 42 degrees C for 200 generations (about one month). These changes in fitness are due to selection on de novo mutations and show that some biological systems can evolve rapidly in response to changes in environmental factors such as temperature.

Biological Evolution↗
PubMed1990

Thermal dependence of locomotor capacity.

The thermal dependence of locomotor performance capacity, particularly speed and endurance, in vertebrate ectotherms is examined. Most studies have found an optimal speed for performance at relatively high body temperatures, close to upper lethal limits. These performance capacities decrease markedly at low body temperatures and may be compensated by increments in aggressive or evasive behaviors. Relative ranking of performance is maintained among individuals across body temperatures. Acclimation of performance capacities is generally incomplete or entirely absent: most animals compensate locomotor performance rather poorly to cold exposure. Locomotor performance in different groups has been shown to possess the attributes (e.g., variability, repeatability, heritability, and differential survivorship) necessary for evolutionary adaptation, but interpretation of comparative data is complicated by phylogenetic differences among species studied. Controlled studies show partial but incomplete adaptation to environmental temperature.

Acclimatization↗
PubMed1990

Quantitative genetics of maximal oxygen consumption in a garter snake.

Broad-sense heritabilities and genetic correlations of maximal oxygen consumption (VO2max), blood hemoglobin levels, and ventricle mass were estimated in a natural population of snakes. Traits were measured for six or fewer presumed full-sibling offspring from each of 45 wild-caught gravid garter snakes (Thamnophis sirtalis). VO2max was highly reproducible between replicate trial days (r = 0.88). In an attempt to reduce maternal effects, correlations of each character with body mass, snout-vent length, age at testing, litter size, dam mass, and dam snout-vent length were removed by computing residuals from multiple-regression equations. These residuals were used in subsequent genetic analyses. Approximate coefficients of variation of residuals were 16% for VO2max, 19% for hemoglobin level, and 13% for ventricle mass. Broad-sense heritabilities were highly significant for all characters [P less than 0.0001; VO2max heritability (h2) = 0.88; hemoglobin level h2 = 0.63; ventricle mass h2 = 0.41], suggesting that they could respond genetically to selection. Phenotypic correlations (rP) among residual characters were significant only between VO2max and ventricle mass (rP = +0.27). VO2max and ventricle mass exhibited a significant (broad-sense) genetic correlation of +0.64; this might facilitate the correlated evolution of these two traits in response to natural or artificial selection. Ventricle mass and hemoglobin level showed a significant environmental correlation of +0.43. Treadmill endurance crawling time (Evolution 42: 335-350, 1988) showed a weak but significantly positive rP with VO2max (rP = +0.17).

Aging↗
PubMed1989

Individual correlation of morphology, muscle mechanics, and locomotion in a salamander.

Measurements were made on locomotor performance (burst run and swim speed, run and swim endurance), morphology (body, tail, and hindlimb length, body mass), and skeletal muscle mechanics (isometric: twitch and tetanic tension, rates of force development and relaxation; isotonic: maximal velocity of shortening and power output) in a size range of individual salamanders (Ambystoma tigrinum nebulosum) at 10 and 20 degrees C. The size dependence of each factor was determined, and the interindividual correlations among factors were measured after removal of size effects. Locomotor performance is positively related to body size: larger animals are faster and have higher endurance. Isometric tensions (standardized for muscle cross-sectional area) and isotonic properties are mass independent; rates of isometric force development and relaxation are negatively related to body mass. Locomotor performance capacities are not intercorrelated among individuals. Isometric force and rates of force development are highly intercorrelated as are maximal shortening velocity and power output. Several statistical techniques failed to uncover correlations among sets of variables (performance, morphology, muscle mechanics): neither fast individuals nor individuals with high endurance necessarily have relatively fast muscles or long limbs or tails after the effects of body size have been removed.

Ambystoma↗
PubMed1988

Evidence that the cytoplasmic aldehyde dehydrogenase-catalysed oxidation of aldehydes involves a different active-site group from that which catalyses the hydrolysis of 4-nitrophenyl acetate.

Acylation of the aldehyde dehydrogenase.NADH complex by acetic anhydride leads to the production of acetaldehyde and NAD+. By monitoring changes in nucleotide fluorescence, the rate constant for acylation of the active site of the *enzyme.NADH complex was found to be 11 +/- 3 s-1. The rate of acylation by acetic anhydride at the group that binds aldehydes on the oxidative pathway is clearly rapid enough to maintain significant steady-state concentrations of the required active-site-acylated *enzyme.NADH intermediate despite the rapid hydrolysis of this *enzyme.acyl.NADH intermediate (5-10 s-1) [Blackwell, Motion, MacGibbon, Hardman & Buckley (1987) Biochem. J. 242, 803-808]. Hence reversal of the normal oxidative pathway can occur. However, although acylation of the aldehyde dehydrogenase.NADH complex by 4-nitrophenyl acetate also occurs rapidly with a rate constant of 10.9 +/- 0.6 s-1, even under the most extreme trapping conditions only very small amounts of acetaldehyde are detected [Loomes & Kitson (1986) Biochem. J. 235, 617-619]. Furthermore enzyme-catalysed hydrolysis of 4-nitrophenyl acetate is limited by the rate of deacylation of a group on the enzyme (0.4 s-1), which is an order of magnitude less than deacylation of the group at the active site (5-10 s-1). It is concluded that the enzyme-catalysed 4-nitrophenyl ester hydrolysis involves a group on the enzyme that is different from the active-site group that binds aldehydes on the normal oxidative pathway.

Acetaldehyde↗
PubMed1979

Endothermy and activity in vertebrates.

Resting and maximal levels of oxygen consumption of endothermic vertebrates exceed those of ectotherms by an average of five- to tenfold. Endotherms have a much broader range of activity that can be sustained by this augmented aerobic metabolism. Ectotherms are more reliant upon, and limited by, anaerobic metabolism during activity. A principal factor in the evolution of endothermy was the increase in aerobic capacities to support sustained activity.

Adaptation, Biological↗