PMN elastases: a comparison of the specificity of human isozymes and the enzyme from other species toward substrates and inhibitors.

The human elastases isolated from polymorphonuclear neutrophils (PMN) and purulent sputum displayed identical kinetic constants toward substrates and inhibitors. The elastases from the two sources yield identical N-terminal sequences and were recognized by antiserum prepared against human sputum elastase (HSE) isozyme-4 (I-4). The data support the proposal put forth by Twumasi and Liener (1977, J. Biol. Chem. 252, 1917-1926) that the human elastase from sputum is of PMN origin. PMN elastases from other species displayed kinetic constants toward both substrates and inhibitors significantly different from the human enzyme. Therefore, extrapolation of inhibitor profiles from these elastases to the human source should be avoided. Four groups of isozymes were resolved from HSE by FPLC. Only the most basic isozyme (I-4) was obtained as a single species. The isozymes displayed identical macroscopic kinetic constants toward several substrates and two classes of inhibitors. The similar partition ratios observed with a cephalosporin-derived inhibitor suggest that the microscopic rate constants are also identical. The data support the proposal suggested by Baugh and Travis (1976, Biochemistry 15, 836-841) that HLE isozymes differ only in carbohydrate content. Whatever the source of human PMN elastase heterogeneity, it does not result in heterogeneous catalytic properties. In addition, a new protein was identified in elastase preparations derived from human sputum. This protein displayed homology to serine proteases and properties suggesting that it is identical to azurocidin.