ATPase activity and proteolysis of human myocardial actomyosin in ischemia and hypertrophy

Recently we have shown that actomyosin ATPase activity decreases with age when measured under appropriate conditions (Yoshida K et al, Age 12: 97-102, 1989). Many previous studies, which examined changes in ATPase activity in myosin, actomyosin, or myofibrils under pathological states, ignored the age-related changes. In this study actomyosin was isolated from myocardia of middle-aged subjects (37-49 years old) and examined for ATPase activity under various conditions and protein composition. Proteolysis of myosin and troponin was more frequently observed in ischemic heart disease (IHD) subjects than in non-IHD subjects. The proteolysis was associated with a decrease in Ca2+ sensitivity of Mg2(+)-ATPase activity and enhanced stimulation of Ca2(+)-ATPase activity with a sulfhydryl reagent, N-ethylmaleimide. Hypertrophy appeared not to significantly affect ATPase activity.