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 ac tivity of chicken fast and slow skeletal muscle myofibrils. In both ty pes of myofibrils the Ca2+-sensitivity declined on decreasing pH from 7.4 to 6.2, but the slow skeletal muscle myofibrils were found to exhi bit a Ca2+-sensitive ATPase activity which was more resistant to acidi c pH compared to the fast skeletal muscle myofibrils. The results obta ined by using a novel method for replacing whole troponin complex in m yofibrils provide the first evidence that troponin is responsible for this higher resistibility of slow skeletal muscle myofibrils to acidos is. (C) 1995 Academic Press, Inc.