Location of the essential thiol of porcine liver cathepsin B.
Porcine liver cathepsin B, a thiol enzyme, exists in at least three forms. While Form III is a single chain polypeptide, two peptide chains with molecular weights of 258000 and 4,000 are noncovalently bound together in Form I and Form II. The present study showed that aminoterminal sequences of Form III and the 4,000-dalton peptide isolated form Form II are identical. The 4,000-dalton peptide contained three cysteine or half-cystine residues, one of which was demonstrated to be essential for the enzyme activity by an incorporation study with [14C]iodoacetate. It was also shown that the 4,000-dalton peptide of the activated enzyme contained one cysteine and one cystine residue.
D000596:Amino Acids / Q000032:analysis; D000818:Animals; D002403:Cathepsins / Q000378:metabolism; D003545:Cysteine / Q000032:analysis*; D003553:Cystine / Q000032:analysis*; D008099:Liver / Q000201:enzymology*; D046911:Macromolecular Substances; D008970:Molecular Weight; D010446:Peptide Fragments / Q000032:analysis; D013552:Swine
D000596:Amino Acids; D046911:Macromolecular Substances; D010446:Peptide Fragments; D003553:Cystine; D002403:Cathepsins; D003545:Cysteine