Polymorphism of cow colostrum proteinase inhibitor

Abstract

Cow colostrum contains three isoinhibitors A, B, and C, which are glycoproteins. In this study isoinhibitor A was isolated and characterized and the structure of its protein moiety compared with the known protein structures of isoinhibitors B and C. It was found that the primary structure of isoinhibitor A is identical with the primary structure of isoinhibitor B except that the C-terminus of its molecule is shorter by five amino acid residues. Four discrete chromatographic forms (I-IV) with different isoelectric points (pI 3.8 - I, 4.0 - II, 4.3 - III, and 4.5 - IV) were isolated by chromatography on SE-Sephadex, Form I is identical with isoinhibitor A. Forms II, III, and IV are represented by mixtures of isoinhibitors A, B, and C with a heterogeneous carbohydrate moiety which affects the total net charge of the individual inhibitor forms.