Structural relationship between human high and low molecular mass urokinase.

Human low molecular mass urokinase was demonstrated to consist of two polypeptides. The peptide chains of about 30000 and of 2427 Da, respectively, were isolated by gel filtration after reductive cleavage of single interchain disulfide bridge. The complete amino acid sequence of the 2427-Da chain consisting of 21 amino acids was determined. Stoichiometric amounts of hexosamines were found in the 2427-Da chain. The isolated 30000-Da chains of both, human low and high molecular mass urokinases were found to be identical in terms of amino acid composition, of hexosamine content, of N- and of C-terminal amino acid sequences. The amino acid sequence of the 2427-Da chain of the low molecular enzyme was found to be different from the N-terminal sequence of the 20000-Da chain of the high molecular enzyme. The transformation of high to the low molecular form is considered a limited proteolytic degradation of the 20000-Da chain of high molecular mass urokinase, exclusively.