[Multiple forms of horse pepsin].

Using ion-exchange and affinity chromatography and isoelectrofocusing, eight forms of pepsin with pI 1.6, 1.8, 2.1, 2.3, 2.6, 2.8, 3.2 and 3.6, were isolated from horse gastric juice. The molecular weights, amino acid composition, N-terminal sequence and functional activity of these multiple forms were determined. Partial primary structure of tryptic peptides of pepsin with pI 2.3 was investigated. The analyzed partial sequences of the forms with pI 1.8, 2.1, 2.3, and 2.6 have identical structures which differ from the amino acid sequence of pepsin with pI 3.2 by four substituents. In terms of their functional activity, horse pepsins differ only insignificantly. Presumably, the pepsins under study (at least the forms with pI 1.8, 2.1, 2.3, 2.6 and 3.2) arose comparatively recently as a result of duplication of the common precursor gene and exist at an early stage of structural and functional divergence. As far as their primary structure and functional properties are concerned, these pepsins are more related to pepsin A than to other isoenzymes of gastric aspartyl proteinases of mammalia, e. g., gastricsin or chymosin.