The substrate specificity of thermomycolase, an extracellular serine proteinase from the thermophilic fungus Malbranchea pulchella var. sulfurea

Abstract

The specificity of thermomycolase toward glucagon and the oxidized A and B chains of insulin was investigated. Extensive digestion of glucagon occurred when conducted at pH 7.0 and 45 ° C for 40 min, whereas hydrolysis of only three peptide bonds occurred at pH 7.0 and 28 ° C for 5 min. A similar situation was observed for the oxidized B chain of insulin, which exhibited only a single major cleavage after 5 min at 25 ° C. No well-defined specificity for particular amino acid residues was evident, but ready hydrolysis of peptide bonds occurred within sequences containing non-polar residues. This endoproteinase must therefore possess an extended hydrophobic binding site for polypeptides. Thermomycolase hydrolysed acetylalanylalanylalanine methyl ester and elastin-Congo Red at 22 and 8.5 times the rate of porcine elastase respectively. A limited degradation of native collagen and significant hydrolysis of benzyloxycarbonyl-Gly-Pro-Leu-Gly-Pro were suggestive of some collagenase-like activity. No keratinase activity was apparent.