Isolation of Acidic Acrosin Isoinhibitors (BUSI I A, BUSI I B1 and BUSI I B2) from Bull Seminal Plasma

Abstract
Three natural proteinase isoinhibitors with low isoelectric points BUSI [bull seminal plasma inhibitor] I A (pI = 3.9), BUSI I B1 (pI= 3.4) and BUSI I B2 (pI = 3.7) were isolated from bull seminal plasma by gel filtration on Sephadex G-50 and ion exchange chromatography on DEAE-Sephadex and SE-Sephadex. Isoinhibitors B1 and B2 have identical amino acid composition. Isoinhibitor A contains 6 amino acid residues less than isoinhibitors B1 and B2. Since sugars were detected in the isoinhibitors, heterogeneity may also be due to the sugar component. The isoinhibitors show the same inhibitory properties; all of them inhibit acrosin, trypsin (EC 3.4.21.4) and chymotrypsin (EC 3.4.21.1). Glandular kallikrein is also inhibited, but to a very low extent only. The MW (.apprx. 8900) was determined by gel filtration.

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