PURIFICATION AND CHARACTERIZATION OF AN EXTRACELLULAR THIOL-CONTAINING SERINE PROTEINASE FROM THERMOMYCES-LANUGINOSUS

An extracellular protease produced by the filamentous fungus Thermomyces lanuginosus has been purified and characterized. The results indicate that the enzyme, which we have called humicolin, is a thiol-containing serine protease with a molecular mass of 38000 kilodaltons. Secretion of humicolin, which is glycosylated, is tightly regulated by protein substrates. Kinetic characterization has revealed that humicolin activity is highly dependent upon the deprotonation of a group with a pK(a) of 6.6 and that the enzyme has a specificity for phenylalanine in the P1 position of the substrate.