The metabolic and biochemical adaptations which set the endurance limit in skeletal muscle and are modified by physical training, and those which set the fatigue limits in conditions of chronic hypoxia, are not completely understood. Therefore, the purpose of this study was to measure the key metabolites involved in the control of oxidative and glycolytic metabolism, during the elevated metabolic demands of exercise, in subject groups which were separated by distinct differences in their training status or by their exposure to chronic hypobaric hypoxia. Since repeated measures of the key metabolites involved in energy metabolism (PCr, Pi, ATP) and intracellular pH (pHm) would be exceedingly difficult using the conventional muscle needle biopsy technique, ³¹P NMR was selected as an appropriate, noninvasive method for measuring these metabolites. Two separate exercise models were developed for use within a 1.0 m bore NMR machine. An electrical stimulation model using the rectus femoris muscle was developed and the factors which influenced reliability and reproducibility of the data were determined. In addition, a dynamic exercise model was developed in which the gastrocnemius muscle was exercised in a mechanical calf ergometer. The results of the experiments using the electrical stimulation model indicate that RF coil geometry, stimulation intensity and duty cycle, electrode placement, and subject tolerance require very close control for the model to be reliable. It is felt that this model is best suited for experiments which require a within-subject design and is ideally suited for experimental or therapeutic intervention studies. The calf ergometer was used to compare sedentary lowlanders, marathon and ultramarathon runners, power trained athletes, and Quechua Indians, native to altitudes of 4,200 m in the Andes, before and after deacclimation to sea level. It was found that the Andean natives did not possess a standard physiological phenotype with respect to aerobic and anaerobic capacities. In addition, given the Andean's very low anaerobic capacity and intermediate aerobic capacity, this group performed calf work equivalent to that of highly trained endurance and power athletes. Moreover, pHm, PCr, Pi, and ATP showed equivalent perturbation at fatigue and in recovery compared with the marathon runners but considerably less perturbation than was found in the power trained athletes who possess equivalent aerobic capacities but far greater anaerobic capacities. NMR derivable estimates of the phosphorylation potential in this study support the theory that closer coupling between ATP supply-ATP demand may be responsible for reduced kinetic and thermodynamic activation of mitochondrial metabolism seen in the Andean natives. / Science, Faculty of / Zoology, Department of / Graduate

Part of Thesis (Ph. D.)--University of Chicago, 1932. / "Private edition, distributed by the University of Chicago Libraries, Chicago, Illinois." Bibliography: p. 11-12.

Part of thesis (Ph. D.)--University of Chicago, 1932. / "Private edition, distributed by the University of Chicago Libraries, Chicago, Illinois." "References": p. 11-12.

Access to abstract permanently restricted to Ball State community only / Access to thesis permanently restricted to Ball State community only / School of Physical Education, Sport, and Exercise Science

Not available / text

There is no abstract available for this dissertation. / Human Performance Laboratory

There is no abstract available for this dissertation. / School of Physical Education, Sport, and Exercise Science

A comparative survey of the maximum catalytic activities in vitro of 2-oxoglutarate dehydrogenase and pyruvate dehydrogenase in muscles throughout the animal kingdom was carried out. Knowledge of the quantitative nature of the TCA cycle enabled the physiological function and metabolic characteristics of these muscles to be discussed in detail (Chapters Four and Five).

The enzymatic organization of muscle tissue usually is examined in only a select few muscles of any one animal species. However, because the functional demands placed on individual muscles can vary so widely from muscle to muscle, it is inappropriate to generalize findings from one or two muscles to muscle tissue in general. The differences or similarities in metabolic machinery between skeletal muscles of a wide functional range provides crucial information with respect to a particular animals' whole body metabolism. Nowhere is this understanding more important than in the diving marine mammal which must operate as a closed system (with respect to oxygen supply) while submerged. The goals of this thesis are: 1) to provide a broad body of information on the metabolic organization of a large cross-section of marine mammal muscles, both functionally and with regard to location, 2) to assess the implications of the enzyme differences between muscles to the diving habit, and 3) to compare the metabolic organization of skeletal muscle among several species of marine mammal with different diving abilities and habits. A series of 13 enzymes were measured in 21 skeletal muscles of the harbor seal, Phoca vitulina. In addition, 23 enzyme activity ratios were calculated and analyzed for these muscles. A similar analysis of 22 muscles from fin whales, Balaenoptera physalis. was conducted --including 7 key enzymes and 15 activity ratios. Overall, both the maximum activities and the enzyme activity ratios are consistent with the idea that marine mammal muscle is typical mammalian muscle, exhibiting few significant differences from terrestrial species with respect to catabolic enzymes. The only obvious exception to this in the species examined is observed with fin whale locomotory muscle which has extremely high activities of lactate dehydrogenase (over 2000 units/gm wet wt at 25°C) due to an apparent scaling phenomenon. Tight control of this high potential glycolytic flux is indicated by pyruvate kinase activities that scale downward. Comparisons of enzyme relationships between muscles of harbor seals seem to indicate a very aerobically poised metabolic make-up. This is especially true with respiratory and locomotory muscles, which also show a high tendency to utilize fat. This pattern of enzyme activities and activity ratios in the locomotory muscles of harbor seal is evidence that muscle contractile activity while diving is powered primarily through oxidative pathways and largely based on fat as fuel. The majority of non-locomotory muscles appear to be more able to function anaerobically utilizing carbohydrate. This pattern may correlate with circulatory redistributions while diving that preferentially fuel the locomotory muscles with oxygen, leaving the inactive muscles significantly more hypoperfused and, therefore, candidates for energy saving O₂ sparing (metabolic depression). Fin whales exhibit an opposite pattern, with enzyme profiles more typical of "white" muscle. Unlike harbor seals, the locomotory muscles of fin whales are consistently the least oxidatively poised of the muscles examined. This apparently more anaerobic nature of fin whale muscle is possibly complicated by scaling adaptations, but appears to be a real phenomenon. The examination of three to four skeletal muscles from each of three additional phocid seal species from Antarctica, leopard seals (Hydrurga leptonyx). crab-eater seals (Lobodon carcinophagus). and Weddell seals (Leptonychotes weddelli) confirm that the harbor seal pattern of enzyme profiles is fairly consistent among phocid seals. By these criteria skeletal muscles of phocid seals (particularly the locomotory and respiratory muscles) appear to be designed for sustained aerobic metabolism during diving regardless of the habits or diving capabilities of the seal. / Science, Faculty of / Zoology, Department of / Graduate

Thesis (PhD)--Stellenbosch University, 2013. / ENGLISH ABSTRACT: It is widely accepted that insufficient insulin-stimulated activation of muscle glycogen synthesis is one of the major components of non-insulin-dependent (type 2) diabetes mellitus. Glycogen synthase, a key enzyme in glycogen synthesis, is extensively regulated, both allosterically (by glucose-6-phosphate, ATP, and other ligands) and covalently (by phosphorylation). Although glycogen synthase has been a topic of intense study for more than 50 years, its kinetic characterization has been confounded by its large number of phosphorylation states. Questions remain regarding the function of glycogen synthase regulation and the relative importance of allosteric and covalent modification in fulfilling this function. The regulation of glycogen synthase and glycogen phosphorylase, the enzyme that catalyses the degradation of glycogen chains, are reciprocal in many respects. In the present research, using mathematical modelling, we aim to establish the function of the allosteric and covalent regulation of glycogen synthase and glycogen phosphorylase in muscle and, in the case of glycogen synthase, the relative importance of these two mechanisms in performing this function. In order to realize these aims it is essential that a detailed kinetic model of glycogen metabolism is constructed. We begin with a thorough review of the kinetics and regulation of glycogen synthase inwhich we propose that both allosteric and covalent modification of glycogen synthase can be described by a Monod-Wyman-Changeux model in terms of apparent changes to L0, the equilibrium constant between the T and R conformers. We then proceed to develop a rate equation according to the proposed Monod-Wyman-Changeux model and determine values for its kinetic parameters from published experimental data using non-linear least-squares regression. We show that the application of the Monod-Wyman-Changeux model to glycogen synthase kinetics also has important implications for the rate equations of enzymes that catalyse the phosphorylation and dephosphorylation of glycogen synthase. We formalize these implications for a generic protein that follows Monod-Wyman-Changeux-type conformational change and then also show how the findings apply to glycogen synthase. Taking into account the kinetic model of glycogen synthase and how it also influences the covalent regulation of the enzyme, we proceed to construct a detailed mathematical model of glycogen synthesis that includes the glycogen synthase phosphorylation cascade. A variation of this model in which glycogen synthase phosphorylation is described with a single parameter is also provided. We reuse an existing model of muscle glycogenolysis and also combine these models in an overall model of glycogen metabolism. Finally, we employ the theoretical frameworks of metabolic control analysis, supply-demand analysis, and co-response analysis to investigate the function of glycogen synthase and glycogen phosphorylase regulation. We show that the function of glycogen synthase regulation is not flux control, as assumed in the textbook view, but rather the maintenance of glucose-6-phosphate within a narrow range far from equilibrium. Similarly, we show that regulation of glycogen phosphorylase functions to minimize variation in cellular energy charge in the face of highly variable energy demand. We conclude with an appeal for a renewed interest in the enzyme kinetics of muscle glycogen metabolism. / AFRIKAANSE OPSOMMING: Daar word wyd aanvaar dat onvoldoende insulien-gestimuleerde aktivering van spierglikogeensintese een van die hoofkomponente van insulien-onafhanklike (tipe 2) diabetes mellitus is. Glikogeensintase, ’n sleutelensiem in glikogeensintese is onderworpe aan breedvoerige regulering, beide allosteries (deur glukose-6-fosfaat, ATP, en ander ligande) en kovalent (deur fosforilering). Alhoewel glikogeensintase reeds vir meer as 50 jaar deeglik bestudeer word, word die kinetiese karakterisering daarvan bemoeilik deur die groot aantal fosforilasiestate waarin die ensiem voorkom. Daar is steeds vrae betreffende die funksie van die regulering van glikogeensintase en die relatiewe bydrae van allosteriese en kovalente regulering in die vervulling van hierdie funksie. Die regulering van glikogeensintase en glikogeenfosforilase, die ensiem wat die afbraak van glikogeenkettings kataliseer, is in baie opsigte resiprook. In hierdie studie beoog ons om met die hulp van wiskundige modellering vas te stel watter funksie die regulering van glikogeensintase en glikogeenfosforilase vervul en, in die geval van glikogeensintase, wat die relatiewe belang is van allosteriese en kovalente regulering in die vervulling van hierdie funksie. Om hierdie oogmerke te verwesentlik is dit nodig dat ’n kinetiese model van glikogeenmetabolisme ontwikkel word. Ons begin met ’n omvattende oorsig van die kinetika en regulering van glikogeensintase waarin ons voorstel dat beide die allosteriese en kovalente regulering van glikogeensintase beskryf kan word met die Monod-Wyman-Changeux model in terme van oënskynlike veranderings aan L0, die ekwilibriumkonstante tussen die T en R konformasies. Ons gaan dan voort om ’n snelheidsvergelyking te ontwikkel volgens die voorgestelde Monod-Wyman-Changuex-model en bepaal ook die waardes van hierdie vergelyking se parameters vanaf gepubliseerde eksperimentele data deur middel van nie-lineêre kleinste-vierkantsregressie. Ons wys dat die toepassing van die Monod-Wyman-Changuex-model op glikogeensintase-kinetika belangrike gevolge het vir die snelheidsvergelykings van die ensieme wat die fosforilering en defosforilering van glikogeensintase kataliseer. Ons formaliseer hierdie gevolge vir ’n generiese Monod-Wyman-Changeux-tipe proteïen en wys dan ook hoe die bevindings op glikogeensintase van toepassing is. Met inagneming van die kinetiese model vir glikogeensintase en hoe dit die kovalente regulering van die ensiem be¨ınvloed, gaan ons voort om ’n gedetaileerde wiskundige model van glikogeensintese, wat ook die glikogeensintase-fosforileringskaskade insluit, te ontwikkel. ’n Variasie op hierdie model waarin die fosforilering van glikogeensintase deur ’n enkele parameter beskryf word, word ook voorsien. Ons herbruik ’n bestaande model van spierglikogenolise en kombineer ook hierdie modelle in ’n oorkoepelende model van glikogeenmetabolisme. Uiteindelik span ons die teoretiese raamwerke van metaboliese kontrole-analise, vraag-aanbod-analise, en ko-responsanalise in om die funksie van die regulering van glikogeensintase en glikogeenfosforilase te ondersoek. Ons wys dat die funksie van die regulering van glikogeensintase nie fluksiekontrole, soos algemeen in handboeke aangeneem word, is nie, maar liewer dat dit glukose-6-fosfaat handhaaf binne ’n noue band ver vanaf ekwilibrium. Insgelyks wys ons dat die regulering van glikogeenfosforilase funksioneer om variasie in sellulˆere energielading te beperk ten spyte van hoogs wisselende vlakke van energie-aanvraag. Ons sluit af met ’n pleidooi vir hernieude belangstelling in die ensiemkinetika van glikogeenmetabolisme in die spier. / National Research Foundation