The isolation and properties of pig submandibular kallikrein

Abstract

The kallikrein from pig submandibular glands was highly purified, with an overall yield of 31%. Affinity chromatography on bovine basic pancreatic trypsin inhibitor linked to Sepharose 4B was an especially effective step in the purification procedure, giving a purification factor of 80. The enzyme is a single-chain molecule, occurring, as does pig urinary kallikrein, as a major B-form of apparent mol.wt. 39600 and minor amounts of an A-form of apparent mol.wt. 35900; the two forms can be separated by sodium dodecyl sulphate/polyacrylamide-gel electrophoresis. The amino acid composition of pig submandibular kallikrein is very similar to, but not quite identical with, that of the two-chain β-kallikrein isolated from pig pancreatic autolysates. Submandibular kallikrein contains notably more glucosamine and hexoses than does pancreatic β-kallikrein. Submandibular kallikrein, and also urinary kallikrein, exhibit an unusual biphasic hydrolysis of substrate esters that is not shared by pancreatic β-kallikrein. For the submandibular enzyme, the Km for the initial reaction phase of the hydrolysis of α-N-benzoyl-l-arginine ethyl ester is 0.15±0.01mm (mean±s.e.m.), but rises to 0.69±0.04mm (mean±s.e.m.) in the stationary reaction phase; the Vmax. does not differ significantly between the two phases. The esterolytic activities of submandibular and urinary kallikreins on a number of esters of different amino acids resemble each other much more closely than those of pancreatic β-kallikrein.