Stability of two Ca2+‐dependent neutral proteinases and their specific inhibitor during post‐mortem storage of rabbit skeletal muscle

The variation in the amounts of the two forms of Calcium Activated Neutral Proteinase (high Ca2+ requiring and low Ca2+ requiring forms) and their specific inhibitor was determined during storage of skeletal muscle at 4°C for 0, 1, 3 and 6 days. Whereas the activity of the high Ca2+ requiring form remained nearly constant during this period, there was a progressive decrease in the levels of both the low Ca2+ requiring form and the specific inhibitor. The effect of different Ca2+ concentration on the two purified forms of the enzyme in the presence and absence of the inhibitor was also examined. Both enzyme forms were labile to preincubation at 30°C without inhibitor in 3 mmol litre−1 Ca2+ whereas in 50 μmol litre−1 Ca2+ only the low Ca2+ requiring form was inactivated, i.e. at a concentration which can be reached in muscle cells during contraction or after death of the animal. When the specific inhibitor was added, preincubation in 3 mmol litre−1 Ca2+ did not affect either enzyme form since they were found to retain full activity on subsequent removal of the inhibitor. A possible role for the Calcium Activated Neutral Proteinases in the development of meat tenderness is discussed.