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Studies of kallikreins. V. Purification and characterization of rat intestinal kallikrein.

Kallikrein [EC 3.4.21.8] was extracted from rat small intestine and purified by acetone fractionation, DEAE-Sephadex A-50 chromatography, Sephadex G-100 gel filtration, hydroxylapatite chromatography, Sephadex G-50 gel filtration and Ampholine isoelectric focusing. Rat intestinal kallikrein (RIK) was separated into 4 or 5 active components and the isoelectric points of the two main fractions were 4.18 (RIK-A) and 4.03 (RIK-B). The final preparations of RIK-A and -B were homogeneous in disc electrophoresis in polyacrylamide gel and their vasodilator activities were 160 and 90 KU per A280, respectively. The molecular weights of RIK-A and -B were estimated by Sephadex G-100 gel filtration to be 33000 and 35000, respectively, while the values obtained by SDS-polyacrylamide gel electrophoresis were both 32000. The amino acid compositions of the two RIK's were similar. The Km values of RIK-A against BAEE and TAME were 0.11 and 0.09 mM, and those of RIK-B were 0.08 and 0.11 mM, respectively. For both RIK-A and -B the optimal pH for hydrolysis of BAEE was 9.2, and both enzymes were stable at pH 7-9. The substrate specificities of RIK-A and -B were similar to that of rat pancreatic kallikrein. Both RIK's were inhibited by aprotinin and leupeptin, but not by SBTI, LBTI, antipain, pepstatin, or chymostatin.