Characterization of pig pancreatic kallikreins A and B.

Pig pancreatic kallikreins A and B are both composed of the same 229 amino acids, a figure resembling the number of amino acid residues found in other serine proteinases of pancreas. Both forms of the enzyme contain N-terminal isoleucine and alanine and C-terminal leucine/serine (about half a mol each per mol kallikrein) and proline. Values for the glucosamine content of the kallikreins obtained on the amino acid analyzer after hydrolysis with p-toluenesulfonic acid, a procedure also used for the determination of amide ammonia, agreed with those determined by a gas-chromatographic method. Neuraminidasetreated kallikrein B differs from the A form only in containing roughly double the amount (on the average a total of 11.5 vs. 5.6% by weight) of carbohydrate (glucosamine, mannose, galactose, and fucose) and possibly by a higher content (20 vs. 17 residues) of amide ammonia. From the composition, molecular weights of 26800 and 28600 are calculated for sialic-acid-free kallikreins A and B, respectively, and of 25300 for the protein part of kallikrein. The molar absorbance of both forms of the enzyme has been determined as (50.6 +/- 1.3) X 10(3)M-1 cm-1 at 280 nm. A comparison of kallikreins A and B with kallikreins d1 and d2 described by Zuber and Sache reveals as principal difference a much lower specific activity of the latter preparations with all reagents tested. Conceivably, the reported lower carbohydrate contents of kallikreins d1 and d2 and their separation into three instead of two major subunits are related to this finding.