Isolation and characterization of native single-chain porcine pancreatic kallikrein, another possible precursor of urinary kallikrein.

Porcine pancreatic kallikrein B' was isolated from partially purified prokallikrein B activated "spontaneously" (most probably due to the action of some contaminating proteinase). Upon dodecyl sulfate electrophoresis after reduction, the enzyme migrated like the single-chain alpha-kallikreins A from submandibular glands and urine of the pig, indicating an apparent molecular weight of about 36,000. Evidently, porcine pancreatic kallikrein B' is also a single-chain alpha-kallikrein, in contrast to the two-chain beta-kallikrein obtained by the usual isolation procedure from autolyzed porcine pancreas. The amino acid composition of kallikrein B' is very similar to that of the other porcine glandular kallikreins and it too contains glucosamine. The specific activities of kallikrein B', as measured under various conditions, also resemble closely those of porcine urinary and submandibular kallikreins, as do the rates of the enzyme-catalyzed hydrolyses of various amino acid ester substrates. During the hydrolysis of Bz-LysOMe or low concentrations of Bz-ArgOEt, the same strange biphasic course of the reaction is seen, as observed previously in the case of the other single-chain porcine kallikreins. Consequently, the properties of native porcine pancreatic kallikrein are well consistent with the suggestion that urinary kallikrein represents filtered enzyme of pancreatic and submandibular origin. Further available evidence for this and the alternative hypothesis of synthesis of urinary kallikrein in the kidney is discussed.