Studies on the frog's sartorius at different stages of activity

Abstract

Myosin was prepared from I g of frog's sartorius muscle and the yield was 20 mg to 30 mg of purified protein per gram wet weight tissue. The extractability of myosin was the same whether the muscle was at rest, in contraction or in fatigue. The adenosine triphosphate concentration was not changed in activity nor in fatigue and thus the extractability of myosin could be related to the unchanged concentration of adenosine triphosphate, but not to the state of activity of the muscle. The adenosine triphosphate activity and the concentration of sulfhydryl groups were the same in pairs of muscles either at rest and in contraction or at test and in fatigue. A fifteen fold decrease in the rate of relaxation of a muscle fatigued by single twitches suggests a progressive change in the relaxing factor system during fatigue.