Oxidation of sarcoplasmic reticulum Ca2+-ATPase induced by high-intensity exercise
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Ca2+-ATPase and Ca2+-pumping activities by the sarcoplasmic reticulum (SR) and the amounts of sulphydryl and carbonyl groups contained in the SR protein were examined in the superficial portion of the gastrocnemius and vastus lateralis muscles of the rat after high-intensity treadmill runs to exhaustion (average time to exhaustion: 363 s). Exercise at the estimated maximal O2 uptake rate led to 16% and 34% reductions in SR Ca2+-ATPase activity (P<0.01) and Ca2+ uptake rate (P<0.01), respectively. The carbonyl group content in SR Ca2+-ATPase, assessed by immunoblotting analysis, was increased by 127% after exercise (P<0.05), while the sulphydryl group content in the purified SR fraction was unchanged. Consistent with the unchanged sulphydryl group content, treatment of homogenates with dithiothreitol, the disulphide reducing reagent, failed to restore the decreased catalytic activity of SR Ca2+-ATPase in exercised muscles. These findings show clearly that high-intensity, exhaustive exercise causes oxidation of SR Ca2+-ATPase protein and suggest that oxidation of amino acids, other than cysteine, in the SR Ca2+-ATPase may be responsible, at least in part, for exercise-induced inactivation of this enzyme.
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