1. It has been observed previously that gastrocnemius muscles from rats rehabilitated after early nutritional stress have low endurance and oxidative capacity (Raju, 1974).2. Exercise during rehabilitation reversed the effects of early malnutrition on muscle function and metabolism. The swimming performance of rehabilitated rats was poor and exercise during rehabilitation improved it.3. The specific activity of gastrocnemius muscle myosin ATP phosphohydrolase (EC 3.6.1.3) was not altered by either early malnutrition or exercise.The gastrocnemius muscles from rats rehabilitated after nutritional stress were observed to fatigue earlier than did those from control animals both in in vitro and in situ studies (Raju, 1974). Increased glycolytic activity and decreased oxidative capacity were also observed in these muscles. Endurance training is known to increase the in situ performance of the muscle (Barnard & Peter, 1971) and its oxidative enzymes (Holloszy, 1967), and this adaptive response was observed even on low-protein diets (Fuge, Crews, Pattengale, Holloszy & Shank, 1968). The activity pattern of rats subjected to early malnutrition has been found to be altered (Frankova & Barnes, 1968). It is possible that poor physical performance of rehabilitated rats reported earlier may be due to relative inactivity of these animals. It was of interest therefore to investigate whether forced physical activity during rehabilitation could reverse the impaired performance and enzyme 'make-up' of muscles of rats subjected to nutritional stress in early life.The alterations in the enzyme profile may be due to alterations in the fibre composition (Raju, 1974). The specific activity of myosin ATP phosphohydrolase (EC 3.6.1.3) (MATPase) may indicate the proportion of slow and fast fibres in the muscle, as the specific activities of myosins from slow and fast muscles differ widely (Barany, Barany, Reckard & Volpe, 1965;Siedel, 1967).In this paper, studies on the swimming performance of rats subjected to early malnutrition and then rehabilitated on a normal diet with and without exercise are reported. Results of the in situ performance of muscles of these rats and the activities of representative glycolytic and oxidative enzymes and specific activity to M-ATPase are also presented. E X P E R I M E N T A LPregnant female rats were maintained on stock colony diet. On the day of delivery, pups from all mothers were pooled and redistributed into two groups. One group of mothers nursed six pups each, while the other group of mothers nursed sixteen pups each (Kennedy, 1957). Dead pups, if any, during the first 3 d were replaced by pups nursed in a similar way. On 22nd day the pups were separated from the mother, and the male pups were maintained in individual cages. All female pups were rejected. Pups nursed in the litter of six/dam were https://www.cambridge.org/core/terms. https://doi
Electron paramagnetic resonance (EPR) spectroscopy of spin-labeled fatty acids was used to investigate their interaction with Escherichia coli-expressed human mitochondrial uncoupling protein UCP2 refolded from inclusion bodies in nonaethylene glycol monododecyl ether (Ct2Eg) micelles. 5-DOXYL-stearic acid and 4-PROXYL-palmitic acid bound to UCP2 exhibited additional clearly separated h § h H "immobile" peaks in the low-and high-field region, respectively, separated by 42 and 44 Gauss, and extensively reduced h+~M, h_~M "mobile" peaks, separated by about 30 G, whereas with 7-DOXYL-stearic acid the I and M peaks were smoothed together into one wide peak. Competition of 4-PROXYL-palmitic acid with added palmitic acid, arachidonic acid, and all-cis-8,11,14-eicosatrienoic acid and of 7-DOXYL-stearic acid with arachidonic acid was indicated by the disappearance of the h+., h_. "immobile" peaks, whereas redist¡ in micelles without protein was indicated by the rising of the h+~M, h_~M "mobile" peaks. In conclusion, a competition of palmitic, arachidonic, and eicosatrienoic acid within a putative fatty acid binding site was observed for mitochondrial uncoupling protein UCP2. This finding together with the observation of EPR spectra of highly immobilized probes exclusively in the presence of the recombinant UCP2 suggest the existence of a fatty acid binding site on UCP2 which is a prerequisite of the fatty acid cycling mechanism as previously postulated for UCP1.
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