Substrate specificity of carp hepatopancreatic cathepsin S for peptides and myofibrillar proteins

From 250 g of carp hepatopancreas, 0.29 mg of the purified enzyme was obtai ned. The bond specificity of cathepsin S for alpha -neoendorphin and neurot ensin was (6)Arg-(7)Lys and (3)Tyr-(4)Glu, respectively. The cleavage sites for insulin B-chain were estimated to be the bonds at (3)Asn-(4)Gln, (6)Le u-(7)Cys, (12)Val-(13)Glu, (13)Glu-(14)Ala, (16)Tyr-(17)Leu, (22)Arg-(23)Gl y, (24)Phe-(95)Phe and (26)Tyr-(27)Thr. P2 position on these peptides were bulky and hydrophobic amino acid residues such as Phe or Leu, small amino a cid residues such as Gly, Ala and Val were also accepted in these positions . Regarding the protein substrates, cathepsin S degraded carp alpha -actini n, actin, tropomyosin and troponins T and I although the proteolyzing speed s were distinct from one another.