TROPONIN ISOFORM DEPENDENT PH-DEPENDENCE OF THE CA2+-ACTIVATED MYOFIBRILLAR ATPASE ACTIVITY OF AVIAN SLOW AND FAST SKELETAL-MUSCLES

The effects of acidic pH were examined on the Ca2+-sensitive ATPase activity of chicken fast and slow skeletal muscle myofibrils. In both types of myofibrils the Ca2+-sensitivity declined on decreasing pH from 7.4 to 6.2, but the slow skeletal muscle myofibrils were found to exhibit a Ca2+-sensitive ATPase activity which was more resistant to acidic pH compared to the fast skeletal muscle myofibrils. The results obtained by using a novel method for replacing whole troponin complex in myofibrils provide the first evidence that troponin is responsible for this higher resistibility of slow skeletal muscle myofibrils to acidosis. (C) 1995 Academic Press, Inc.