Multiple forms of the serine protease Alp of Aspergillus fumigatus

Alkaline proteases were produced by a virulent strain of Aspergillus fumigatus during growth on media containing glucose and proteins or peptides. After isoelectric focusing, six bands of proteolytic activity were detected with synthetic substrates after blotting on nitrocellulose membranes. The main protease (pI = 8.6) corresponded to the known subtilisin-like protease Alp of A. fumigatus and five minor components had lower isoelectric points (8.1 to 5.2). All proteases were produced on different media and in various phases of growth with only small quantitative variations. They also had identical pH optima, were denatured above 45 degrees C and stabilized by Ca2+ ions, were affected by the inhibitors of serine proteases only and had nearly identical substrate specificity against 13 synthetic substrates. On gel chromatography the three most acidic components had higher molecular weights than the main enzyme Alp. It remains to be determined if the enzymes under study arise through posttranslational processing of the main protease or are true isoenzymes, products of a gene family.