Reinigung und Eigenschaften von Dorschmuskel-Kathepsin

Abstract

The main catheptic component of cod muscle was purified 3000-times. The enzyme fraction does not cleave dipeptides or synthetic peptide derivates of the Bergmann-Fruton series. The pH optimum was 4,6. The activity is not influenced by metal ions. The enzyme contains [long dash]with an approximate molecular weight of 50,000 [long dash]two SH-groups per mol which, however, are inactive catalytically. Serine also does not participate in the active site (no inhibition by diisopropylfluorophoshate) whereas histidine is involved in the catalytic process (photooxydation). Cod muscle cathepsin, which acts like an endopeptidase, splits several proteins. The products are peptides with an average chain length of 4.5 residues and free amino acids. The degradation of the B chain of insulin leads to the recognition of two major cleavage sites (15/16 and 16/17); this is in agreement with analyses of cleavage products from hemoglobin. Therefore, cod muscle cathepsin is different from cod spleen cathepsin, and despite some similarities, it is also profoundly different in proteolytic specifity from chymotrypsin and pepsin. A hypothesis is advanced which may explain the biological significance of cathepsin from cod muscle.