The structure of streptokinase I. Cyanogen bromide fragmentation, amino acid composition and partial amino acid sequences

Abstract

1. 1. A highly purified streptokinase preparation has been analysed for amino acid composition and terminal amino acids. It has been found to contain all common amino acids except cysteine and cystine. The N-terminal amino acid sequence has been demonstrated to be isoleucyl-alanyl-glycyl-. As C-terminal amino acid lysine has been found. 2. 2. This streptokinase contains four methionine residues per molecular weight of 48 000. In agreement with this, cyanogen bromide cleavage has given rise to five fragments. These fragments have been isolated by means of gel filtration on Sephadex. 3. 3. The cyanogen bromide fragments have been characterised by amino acid composition, N-terminal amino acid sequence, C-terminal amino acid and molecular weight. One of the fragments had the same N-terminal tripeptide sequence as the whole streptokinase, and therefore represented the N-terminal section of the whole structure. One fragment contained no homoscrine, and had the same C-terminal amino acid as streptokinase, and was thus derived from the C-terminal section of the whole structure. The order of the other three fragments remains to be elucidated.