Effect of sulfhydryl group modification on age-associated alteration of actomyosin ATPase activity in human myocardium.

Cardiac ventricular actomyosin was prepared from autopsy samples from humans ranging in age from one to 83 years, and its Ca2(+)-ATPase and K(+)-EDTA-ATPase activities were determined in the presence or absence of a sulfhydryl reagent, N-ethylmaleimide (NEM). The Ca2(+)-ATPase activity increased in the presence of appropriate concentrations of NEM. The extent of the stimulation of Ca2(+)-ATPase activity by NEM decreased significantly with age. The ratio of K(+)-EDTA-ATPase activity to Ca2(+)-ATPase activity also decreased with age. This suggests that there is an age-related modification of sulfhydryl groups in the myosin molecule.