CATHEPTIC ACTIVITY OF FISH MUSCLE

Catheptic activity was found to be localized in the lysosomal fraction of skeletal muscle of winter flounder (Pseudopleuronectes americanus). The enzyme hydrolyzed hemoglobin, globin, bovine serum albumin and endogenous proteins. The hemoglobin splitting activity of the enzyme under different conditions was determined by gel electrophoresis. An optimum pH of 4.0 was found for both the hemoglobin breakdown and autolytic activity on the endogenous proteins. The enzyme was highly thermostable, dialysis had no effect on its activity, and the enzyme was inhibited by sodium chloride, cysteine, ATP, NAD and phenyl methyl sulfonyl fluoride. Its molecular weight was found to be about 32,000 using sucrose gradient centrifugation.