Intracellular distribution of fish muscle alkaline proteinase

1. Intracellular distribution of a muscle alkaline proteinase was investigated on four kinds of fish. 2. The total activity of the muscle proteinase of carp, Cyprinus carpio, was larger in both myofibrillar (Mf) and microsomal (Mic) fractions than the activity in mitochondrial, lysosomal, and supernatant fractions. The activity found in Mf fraction seemed to due to the Mic enzyme which was not separated from Mf fraction. 3. The relative specific activity was mostly found in Mic fraction in the species tested. 4. The results indicate that the distribution pattern of fish muscle alkaline proteinase is different from those of cathepsin D and acid phosphatase. 5. The Mic fraction hydrolyzed Mf and sarcoplasmic proteins. The rates were 40 and 55%, respectively, of the rate when casein was used as a substrate.