Chemically skinned single fibres from soleus (slow) and tensor fascia latae (fast) muscles of the euthyroid rat and guinea-pig generated maximal isometric tensions in a narrow range of 125 - 150 kN/m2 at a temperature of 25 °C and a sarcomere length of 2.75 μm. The maximum velocity of shortening (Vmax) of the tensor fascia latae (TFL) muscle fibres from the euthyroid rat (12.35 +/- 0.95 LoS-1 - Fibre lengths per second) and guinea-pig (9.93 + 1.14 LOS-1 ) were 2-3 fold higher (P < 0.05, unpaired t-test) as compared to the soleus muscle fibres of the euthyroid rat (5.61 +/- 0.54 LoS-1 ) and guinea-pig (3.92 + 0.35 LoS-1 ) respectively. This was consistent with previous (e.g. Reiser et al., 1985a, b) results on slow and fast muscle fibres. Storing bundles of soleus or TFL muscle fibres from euthyroid rats and guinea-pigs for short (weeks) or long term (months) resulted in significant (P < 0.05, unpaired t-test) reductions in both the maximum isometric tension (Po) and Vmax of stored single fibres in comparison to fresh single fibres. Therefore, all subsequent experiments were done using fresh single fibres. The maximum isometric tension of chemically skinned single fibres from the soleus of mildly hyperthyroid animals (rats), was lower than that generated by equivalent fibres from mildly hypothyroid animals (127.12 +/- 5.87 kN/m2vs. 169.02 +/- 6.62 kN/m2, P < 0.05, unpaired t-test). There was a corresponding reduction in tension production in TFL fibres comparing hyperthyroid with hypothyroid animals (121.30 +/- 6.80 kN/m2 vs. 142.73 +/- 6.38 kN/m2, P < 0.05). On the other hand, Vmax of single fibres from soleus muscles of hyperthyroid rats was higher than the hypothyroid counterparts (6.58 +/- V 0.32 LoS-1 vs. 5.52 +/- 0.27 LoS-1 , P < 0.05, unpaired t-test). Similarly, Vmax of hyperthyroid single TFL fibres was higher than the hypothyroid counterparts (13.81 +/- 0.50 LoS-1 vs. 11.18 +/- 0.65 LoS-1 , P < 0.05). These differences between the hyper- and hypothyroid results - within each muscle type - were observed in the same type of fibre as identified histochemically. These were the slow oxidative (SO) fibre type from the soleus and the fast glycolytic (FG) fibre type from the TFL muscles. It is postulated that the differences in PO and Vmax were due to alterations in the isoforms of the myosin molecule and more specifically to the myosin light chains. Mild dysthyreosis showed that single muscle fibres of the same histochemical type can generate heterogeneous tension/pCa (T/pCa) relationships.

A brief history of fish biomechanical studies is given and a general introduction on the composition and functional properties of fish muscle, in relation to different swimming activities is presented. Thermal adaptations in teleost fish over both evolutionary and seasonal time scales are discussed at different levels of biological organisation. Chapter 2 The isometric properties of live fast fibres, isolated from the abdominal myotomes of the short-horned sculpin (Myoxocephalus scorpius) were examined at temperatures of 5, 10 and 15°C. The properties of fibres isolated from laboratory-acclimated (5 and 15°C) and naturally-acclimatised, summer (July - September) and winter (January - March) fish were compared to assess the modulating effect of environmental factors other than temperature. Chapter 3 Live fast fibre bundles were isolated from the abdominal myotomes of naturally acclimatised (summer and winter) and laboratory acclimated (5°C and 15°C) sculpin. Force-velocity (P-V) characteristics of the fibres were investigated using iso-velocity releases. The mechanisms behind the acclimatory increases in power output in summer and 15°C-acclimated fish, at 15°C are partly due to increases in the Vmax of the fibres. More importantly force generating capacity shows a major acclimatory adaptation which greatly enhances power output at warm temperatures. Chapter 4 Short-horned sculpin were acclimated to either 5 or 15°C (12 h light: 12 h dark) for 6 - 8 weeks. Prey-capture of Crangon crangon was filmed at 200 frames s-1, using a high speed video. The fish employed the three classic kinematic stages as described by Weihs (1973) in a typical "S" shaped fast start. The kinematics of the fast start were unaffected by temperature or acclimation state. 5°C-acclimated sculpin were tested at 5, 10 and 15°C. Rates of acceleration doubled in the 5°C-acclimated fish between 5 and 15°C. Tail-beat frequency also increased significantly from 5.5 Hz at 5°C to 8 Hz at 15°C. However, mean and maximum velocity and tail-beat amplitude were relatively independent of test temperature. Chapter 5 Fast muscle fibres were isolated from rostral and caudal myotomes of summer-caught, short-horned sculpin. Muscle strain patterns for three positions (0.31L, 0.52L, 0.77L) along the body were calculated from changes in body curvature, during fast-starts at 15°C. Isolated rostral and caudal muscle fibres were subjected to the in vivo strain fluctuations and stimulated with a similar duty cycle (25 - 32%) to that found in vivo. Work loops were generated by plotting force and length. The effect of varying muscle stimulation phase on power output and force generation was investigated. At the anterior position in the body the rostral fibres produced significantly greater force (41.9 kN m-2) compared to the caudal fibres (12.2 kN m-2). Similarly, power output at position 1 was also significantly greater in rostral fibres (28.0 W kg-1) compared to caudal fibres (3.7 W kg-1). No difference was found in the properties of the fibres at positions 2 and 3. This suggests that the rostral fibres have adapted to their local mechanical environment to increase force and power generation, although the mechanisms responsible are unknown. Chapter 6 The major findings of this thesis are discussed relating different aspects of muscle performance to locomotory capabilities of sculpin. Thermal adaptations over the natural environmental temperature range encountered by sculpin are considered and the possible mechanisms involved are discussed. Finally, suggestions for elucidating the molecular mechanisms behind adaptations in the shortening speed and force generation are presented.

Chapter 1. A general introduction into the adaptation of teleost fish to changing thermal environments. The underlying mechanisms at all levels of organization are reviewed in relation to adaptive change over evolutionary and seasonal time-scales. Chapter 2. 1. The contractile properties of swimming muscles have been investigated in marine teleosts from Antarctic (Trematomus lepidorhinus, Pseudochaenichthys georgianus), temperate (Pollachius virens. Limanda limanda. Agonis cataphractus. Callionymus lyra) and tropical (Abudefduf abdominalis, Thalassoma duperrevi) latitudes. 2. Small bundles of fast twitch fibres were isolated from anterior myotomes and/or the pectoral fin adductor profundis muscle (m.add.p). Live fibre preparations were viable for several days at in vivo temperatures, but became progressively inexcitable at higher or lower temperatures. The stimulation frequency required to produce fused isometric tetani increased from 50Hz in Antarctic species at 0°C to around 400 Hz in tropical species at 25°C. Maximum isometric tension (P0) was produced at the normal body temperature (NBT) of each species (Antarctic, 0-2°C; North Sea and Atlantic, 8-10°C; Indo-West Pacific, 23-25°C). P0 values at physiological temperatures (200-300 kN m-2) were similar for Antarctic, temperate and tropical species. 3. A temperature induced "tension hysteresis" was observed in muscle fibres from the temperate and Antarctic species. Chapter 3. 1. Fast and slow muscle fibres were isolated from the myotomes of atlantic cod (Gadus morhua L.) and short-horned sculpin (Myoxocephalus scorpius L.). 2. Epinephrine was found to have no effect on twitch or sub-tetanic contractions in fast muscle fibres. 3. Isoprenaline (10-6M) had no effect on the contractility of slow muscle fibres. 4. In contrast, epinephrine elicited a dose-dependent decrease in the half-time for twitch relaxation (t1/2r), and in most cases a decrease in twitch amplitude. Chapter 4. 1. Fast muscle fibres were isolated from the abdominal myotomes of the short-horned sculpin, Myoxocephalus scorpius L. Sinusoidal length changes were imposed about resting muscle length and fibres stimulated at a selected phase during the strain cycle. The work output per cycle was calculated from the area of the resulting force- position loops. Chapter 5. 1. Bundles of 20-30 fast muscle fibres were isolated from the abdominal myotomes of the short-horned sculpin (Myoxocephalus scorpius L.). 2. The energy cost of contraction was measured during oscillatory work at 4°C and 15°C following treatment with iodoacetate and nitrogen gas to block glycolysis and aerobic metabolism. 3. Isolated fibres were subjected to sinusoidal length changes about in situ resting length and stimulated at a selected phase in the strain cycle. Preliminary experiments with untreated preparations established the strain amplitude and stimulation parameters required to maximize work output over a range of cycle frequencies at 4°C and 15°C. Chapter 6. The results of the thesis are discussed, particularly in relation to their evolutionary and locomotory significance. From the principles and ideas formulated, future lines of research are suggested.

No description available.

During C. elegans embryogenesis, myoblasts initially form two rows along the left and right lateral midlines and at ~290 min of development migrate dorsally and ventrally to form the four muscle quadrants present upon hatching (Sulston et al, 1983). As the myoblasts migrate they are still dividing, as are many other cells in their immediate environment. This means the cell-cell contact of cells during migration is dynamic and can vary from animal to animal (Schnabel et al, 1997). This situation creates an environment where the extracellular matrix (ECM) and cell surface contacts are in constant flux, which begs the questions as to how these cells navigate unerringly to their final destination. In an attempt to identify genes mediating these migrations, I performed an RNAi based screen targeting 776 genes predicted to be members of the extracellular matrix (ECM), or one of its receptors. Using both feeding and injection based RNAi, I was able to identify three genes of interest. Knockdowns of F56B3.2 resulted in paralyzed animals with detached muscle, making it a good candidate for a new component of the muscle attachment complex. F33G12.4 knockdowns resulted in an embryonic arrest phenotype with an abnormal muscle lineage, possibly stemming from polarity defects. The only knockdown that resulted in muscle migration defects was that for lam-2, which encodes for the laminin gamma subunit. Analysis of the lam-2 knockdown, as well as knockdowns for the other laminin subunits, revealed dorsal/ventral migration defects as well as a posterior displacement of the anterior-most ventral muscle cells. Investigation of this posterior displacement has led to the identification of a previously un-described anterior muscle migration event and its dependency upon the extension of muscle processes from the leading cells. / Medicine, Faculty of / Medical Genetics, Department of / Graduate

There is a dearth of knowledge on the functional organization of the anatomically complex human masseter muscle. Limited physiological studies suggest a functional organization which may differ significantly from human limb muscles. The present studies aimed to examine the putative relationship between structure and function in the human masseter muscle as a basis for understanding function and dysfunction in human jaw muscles. In the first experiment single motor unit (SMU) activity was recorded from pairs of recording sites distributed throughout the masseter muscle. In each case SMU activity at a chosen location was used as a reference to search for synchronized SMU activity at another selected site. The locations of the needle tips were estimated in 3-dimensions (3-D) by means of an optical system, then transferred to 3-D reconstructions derived from Magnetic Resonance images. This approach permitted calculation of the linear distances between verified muscle recording sites. The mean separation of the sites from which synchronous SMU activity could be recorded was 8.8±3.4mm. The putative territories had a preferred orientation in the antero-posterior axis. Motor unit territories were larger than described previously, and appeared to be related to anatomical compartments. The second experiment involved recording activity from stereotactically mapped masseter SMUs. In each case, the lowest sustainable firing frequency (LSFF) was reached by slow increases and decreases in voluntary firing rate, followed by sustained firing at the lowest possible rate. Pulse-discrimination and digital sampling of consecutive inter-spike intervals (ISIs) were then used to measure LSFF for 2-6 separate occlusal and postural tasks to which each unit contributed. There were significant differences between mean ISIs for the tasks performed by most units, which suggests descending drive to masseter units is highly task-dependent. There were also regional differences in unit task specificities. In the third paradigm, reflex SMU activity was recorded from units in the masseter muscle and the inferior head of the lateral pterygoid muscle. Bipolar electrodes fixed to the gingiva near the maxillary canine delivered single pulses of 1ms duration at sub-noxious levels of intensity. At constrained firing frequencies (10, 15Hz), pulses were injected sequentially, with increasing delays, after preselected spikes. More profound inhibition occurred in units firing at 10 than 15Hz. There were significant differences in masseter inhibitory responses when the unit task varied. Reflex inhibition in masseter and lateral pterygoid SMUs is highly frequency-dependent, and also task-dependent in masseter units. The fourth study involved recording activity from SMUs in the masseter muscle. A midline load cell was fixed to the incisor teeth and aligned either perpendicular (P) or 30 degrees anterior (A) to the occlusal plane, without altering jaw position. A rigid spike-triggered averaging (STA) paradigm was used to extract the contribution of individual SMUs to the overall force at load cell orientations P and A. Spikes preceded or followed by an interval of less than 100ms were rejected prior to averaging. At background bite forces from 0.06-8N, the isometric forces apparently developed by individual units varied randomly with load cell orientations, (P range 36.2±19.6mN; A range 38.2±28.4mN). All units could be fired slowly with varying degrees of muscle coactivation, in some instances without contact on the load cell. The use of STA as a method for determining SMU tension in the masseter muscle appears to be task-dependent and in the presence of coactivation may be inappropriate. The findings collectively indicate the heterogeneous nature of SMU behaviour in the human masseter muscle which is consistent with internal muscle compartments based on anatomical features and functional behaviour. There thus appear to be both physiological and anatomical substrates for differential motor control of selected regions of the human masseter muscle. / Dentistry, Faculty of / Graduate

The effects of epinephrine and electrical stimulation on the activation of glycogen phosphorylase were studied in isolated rat diaphragm and frog sartorius, and rat gastrocnemius in vivo. The resting ratio of phosphorylase, as expressed by the ratio of phosphorylase a to total phosphorylase (-AMP/+AMP ratio) was found to be low of the order of 0.05 in diaphragm and sartorius. In rat gastrocnemius this value was high at 0.26. As measured by the ratio of activity at pH 6.8 to that at pH 8.2 (pH 6.8/8.2 ratio), phosphorylase kinase was essentially in its inactive form under conditions of no stimulation. On treatment with epinephrine, phosphorylase was activated, and there was a significant increase in the activity ratio for phosphorylase kinase, up to 10-fold, indicating that conversion of nonactivated kinase to its activated form had occurred. Epinephrine also produced marked increases, up to 15-fold, in the tissue levels of adenosine 31, 51-monophosphate (cyclic AMP). When muscle was induced to contract by electrical stimulation, phosphorylase was markedly and rapidly activated. In contrast to the effect of epinephrine, electrical stimulation produced no conversion of phosphorylase kinase to its activated form as measured by the pH 6.8/8.2 ratio. This was found for both direct and neural stimulation, at various frequencies, for different times of stimulation, in vitro and in vivo, and in two species. No increase in the tissue levels of cyclic AMP were detected on electrical stimulation. It was concluded that the mechanism of activation of phosphorylase during electrical stimulation is basically different from that produced by adrenergic amines. The data strongly suggests that during muscle contraction phosphorylase is activated by a mechanism which does not involve conversion of phosphorylase kinase to its activated form. In further work, the relationship between phosphorylase activation and muscle contraction was studied. It was found that for any given frequency of stimulation, phosphorylase was activated within 2 sec to a particular ratio for that frequency. On further stimulation, the ratio did not increase. When the temperature was lowered, the steady state phosphorylase ratio for a given frequency was lowered, but activation still occurred rapidly. In experiments in which calcium was removed from the medium by using chelating agents, a correlation was demonstrated between phosphorylase activation and contractile tension. From these results it appears that the mechanism of phosphorylase activation is closely coupled to the contractile mechanism. It is proposed that calcium ion, which is important in excitation-contraction coupling and tension development, is responsible for phosphorylase activation. It is further suggested that calcium ion released into the myoplasm may act with nonactivated phosphorylase kinase to catalyse the conversion of phosphorylase b to phosphorylase a. / Medicine, Faculty of / Anesthesiology, Pharmacology and Therapeutics, Department of / Graduate

Cation sensitive glass microelectrodes were inserted into single striated muscle fibers of the giant barnacle, Balanus nubilus, to measure directly the activities of sodium and potassium in the myoplasm. The total sodium and potassium content of the individual experimental fibers was determined by flame photometry. From these measurements, the percentage of sodium in the fiber which did not affect the microelectrodes and the percentage of water in the fiber which was not available to act as solvent for the potassium ions were calculated. The minimal percentages of "bound" sodium and water were 84% and 42% respectively. It was hypothesized that a significant fraction of this "bound" sodium was involved in ion pair formation with carboxyl moieties on the myosin molecules which comprise the thick filaments, and experiments were designed to test this hypothesis. In the second series of experiments, the activities of sodium, potassium and hydrogen in the myoplasm were measured as the temperature of the solution bathing the fibers was increased from 7 to 40°C. An irreversible shortening occurred in all fibers between 37 and 40°C. When the fibers shortened in a sodium free Ringer solution, the mean activity of sodium increased by 130%, the mean activity of potassium remained relatively constant, and the pH decreased from 7.17 to 6.77. These experiments provided strong evidence that sodium is bound to myosin in the living fiber, for extracted myosin is known to denature at 37°C and release its associated alkali metal cations. In the third series of experiments, the optical density, O.D., of the single striated muscle fibers was measured at 50 mµ intervals between 450 and 850 mµ. At all wavelengths, the O.D. decreased markedly when the normal Ringer bathing solution was replaced by sodium free sucrose Ringer. For example, at 850 mµ the O.D. of the fibers, relative to the initial value in normal Ringer, decreased from 1 to 0.21 ± 0.06 in 25 minutes. The corresponding increase in the transmittance, T, (O.D. = -log T) was from 5% to 55%. This change in O.D. could be reversed by returning the normal Ringer bathing solution to the bath. Large, reversible decreases in O.D. were also observed when potassium and tris were used as substitutes for sodium. These changes in O.D. are explained by the theory of light scattering if it is assumed that sodium is bound to the main scattering centers in the myoplasm, the thick filaments. When the fibers were bathed in sodium free, lithium substituted Ringer, a small reversible increase in the O.D. was observed, which may indicate that lithium is complexed more strongly than sodium to the binding sites on the thick filaments. In the final series of experiments, the number of sodium and potassium ions "bound" to the contractile proteins in a glycerinated fiber was measured. The free concentrations of hydrogen, sodium and potassium were maintained at values similar to those found in an intact fiber. The results indicated that substantial binding of both sodium and potassium occurred, and that proportionally more sodium than potassium ions were "bound". If the results are extrapolated to the intact fiber, they imply that about as much sodium is "bound" to the contractile proteins as is free in the myoplasm. This amount of "bound" sodium is sufficient to explain the results of the denaturation and light scattering experiments, but insufficient to account for the anomalously low activity of sodium in the myoplasm, as measured by a sodium sensitive microelectrode. Thus, it was concluded that either some factor must enhance the binding of sodium to the contractile proteins in a living cell, or that sodium must be sequestered in organelles which are destroyed by the glycerination process. / Medicine, Faculty of / Graduate

The mechanism of rabbit skeletal muscle phosphoglucomutase (EC.2.7.5.1) has been investigated using fluorinated and deoxygenated substrate analogues. Each of the analogues in which the non-acceptor hydroxyls are replaced by fluorine or hydrogen are substrates of the enzyme. The kinetic constants of these substrates are reported. The rate of the mutase reaction of each substrate analogue in the presence of glucose 1,6-diphosphate is the same as that of the half reaction involving production of the fluorinated and deoxygenated glucose 1,6-diphosphate species. The exceptions are 3-fluoro- and 3-deoxy-glucose 1-phosphate, in which cases the rates of the half reactions are 8 times that of the overall mutase reaction. The Km of 3-fluoro-glucose 1,6-diphosphate is approximately 90 times that of glucose 1,6-diphosphate and the other deoxy and fluoro analogues. The inhibition of phosphoglucomutase by fluorinated and deoxygenated substrate analogues has been investigated. The synthesis of a series of novel disubstituted inhibitors (based on glucose 1-phosphate) in which the C-6 hydroxyl is replaced by fluorine and a sugar ring hydroxyl is replaced by either hydrogen or fluorine is described. The inhibition constants show that the hydroxyl distal to the acceptor hydroxyl is most important in the formation of a strong enzyme-inhibitor complex. The synthesis is described of three phosphorofluoridate analogues of glucose phosphate substrates. These analogues were found to only weakly inhibit phosphoglucomutase. No evidence of any phosphoryl transfer between the phosphoenzyme and the phosphorofluoridate analogues could be detected. Thus phosphoglucomutase has a strict requirement for a doubly negatively charged substrate phosphate group. The interaction of phosphoglucomutase with fluorinated substrates and inhibitors has been investigated by ¹⁹Fnmr. Large downfield changes in the chemical shifts of the inhibitors 6-fluoro-glucose 1-phosphate and α-glucosyl fluoride 6-phosphate were found to accompany binding to the phosphoenzyme. The effects of the binding of activating and non-activating metal ions on these spectra were investigated. The different effects observed may be directly related to the chemical basis for the metal induced activation of the enzyme. ¹⁹Fnmr data consistent with a 10² to 10³ fold increase in the tenacity with which phosphoglucomutase binds substrates and inhibitors in the presence of Li⁺ were observed in the spectra of the phosphoenzyme with difluorinated glucose 1-phosphate inhibitors. Two enzyme bound species were detected in the ¹⁹Fnmr spectra of the complexes formed by reaction of the Cd²+ phosphoenzyme with 2- and 3-fluoro-glucose phosphates. These species are tentatively assigned as the fluoro-glucose 1,6-diphosphate species bound in two different modes to the dephosphoenzyme. Only one bound species was observed in the case of 4-fluoro-glucose phosphates. The environment of each substrate glucose hydroxyl in the active site was probed using ¹⁹Fnmr and the fluorinated glucose phosphate substrates. Data inconsistent with a minimal motion type of mechanism (W.J. Ray, A.S. Mildvan & J.W. Long, Biochemistry 1973,12, 3124) were obtained. The results of the nmr and kinetic studies are consistent with an exchange type of mechanism in which the C-3 hydroxyl plays an important role in the reorientation of the glucose 1,6-diphosphate. The data also suggest that there are two distinct glucose binding sites, one for each substrate and glucose 1,6-diphosphate bound in the same mode. / Science, Faculty of / Chemistry, Department of / Graduate

Anaerobic metabolism in cephalopod muscle and in bivalve adductor muscle depends on the coupling of carbohydrate and amino acid metabolism. In cephalopod muscle this is acheived by octopine dehydrogenase (E.C.1.5.1.11) , whereas in the oyster adductor muscle it is acheived by transaminases and malate dehydrogenase (E.C.1.1.1.37). Therefore studies of the catalytic properties (a) of octopine dehydrogenase from muscle of a group of cephalopods, and (b) of cytoplasmic aspartate aminotransferase (E.C.2.6.1.1) and malate dehydrogenase from adductor muscle of the oyster, Crassostrea gigas, were undertaken. Higher activities of octopine dehydrogenase were found in the mantle of Octopus ornatus than in the mantle of Symplectoteuthis oualaniensis, but the catalytic properties of both enzymes were similar. The affinity for pyruvate was low (Km approx. 1.7 mM), but increased with increasing concentrations of arginine; the affinity for arginine similarly increased with increasing concentrations of pyruvate. Octopine dehydrogenase from the spadix muscle of the chambered nautilus, Nautilus pompilius, had a higher affinity for pyruvate (Km approx. 0.3 mM), and this was also increased by increasing arginine concentrations. It is suggested that octopine dehydrogenase maintains redox balance in a manner analogous to lactate dehydrogenase (E.C.I.1.1.27), and closely couples glycolysis with arginine phosphate metabolism, such that an anaerobic reserve is provided for high intensity "burst" work. The octopus mantle relies on this mechanism more so than does the mantle of the oceanic squid, S. oualaniensis, and the Nautilus spadix muscle appears to use this anaerobic process for most of its energetic requirements. In contrast to cephalopod muscle, oyster adductor muscle maintains redox balance through coupling aspartate and alanine metabolism with carbohydrate fermentation. Adductor aspartate aminotransferase had a higher affinity for aspartate than for glutamate, and a higher affinity for 2-ketoglutarate than for oxaloacetate, suggesting that it would function more readily in the direction of aspartate utilization. Adductor malate dehydrogenase had a higher affinity for oxaloacetate than did aspartate aminotransferase, hence the major fate of oxaloacetate produced would be conversion to malate, and this would direct the flow of aspartate carbon towards succinate. Since adductor alanine aminotransferase (E.C.2.6.1.2) is kinetically adapted for alanine formation, these enzymes couple glycolysis with aspartate mobilisation, such that alanine is formed from glucose and succinate from aspartate. In addition,it was found that pyruvate had another possible fate during anoxia in the adductor, that is conversion to an as yet unidentified compound that is produced by a dehydrogenase requiring NADH, alanine and pyruvate as substrates. This enzyme has an extremely low affinity for alanine, and is potently inhibited by succinate at low pH; hence during anoxia production of this compound would be limited, and the pathway leading to succinate production favoured. / Science, Faculty of / Zoology, Department of / Graduate