The action of a muscle proteinase on the myofibrillar proteins of bovine muscle

Myofibrillar proteins from bovine muscle have been treated with a Ca²⁺ activated muscle proteinase and the consequent changes in these proteins have been examined by various techniques. Tropomyosin, α-actinin and troponin were substrates for the enzyme, the last losing its property of inhibiting actomyosin ATPase in the absence of Ca²⁺ ions. Actin and actomyosin were apparently not digested but the Mg²⁺-activated ATPase activity of actomyosin was less after treatment whereas the Ca²⁺-activated ATPase was unaffected. It is suggested that the observed destruction of the Z-bands of the myofibrils by this proteinase is due to its digestion of the α-actinin, rather than the actin component.