Cleavage of the Arg-Ile bond in the native polypeptide chain of human pancreatic stone protein.

The pancreatic stone protein (PSP) isolated from calculi (Mr 14,000) and the 5 protein forms (PSP S1-5) detected in pancreatic juice (Mr 14,000-19,000) derive from the same source differing seemingly in their carbohydrate contents or/and in their polypeptidic chain lengths. This kind of protein would inhibit in vivo CaCO3-crystal growth in pancreatic juice. PSP and PSP S1 N-terminal sequences are identical (NH2Ile-). This report demonstrates that: in PSP S2-5 the amino-terminal is blocked; the C-terminus is alike in every form; the single polypeptide chain of PSP S2-5 is converted into that of PSP S1 or PSP by the specific trypsin cleavage of the Arg-Ile bond.