Properties of a purified proteinase from the yeast Candida albicans

The proteinase from culture supernatants of Candida albicans strain CBS-2730 was purified virtually to homogeneity by ion-exchange chromatography and affinity chromatography. The enzyme consists of a single polypeptide chain with tryptophan at the N- and leucine at the C-terminus. Its molecular weight is approx. 45,000 and the isoelectric point is at pH 4.4. With albumin as a substrate an apparent Km was determined to be 7 . 10(-5) M. The enzyme is inhibited by pepstatin at equimolar ratio and thus is a carboxyl proteinase (EC 3.4.23.6). Other group-specific inhibitors, though, did not efficiently block the enzyme. Above pH 8.4 the enzyme undergoes alkaline denaturation which is accompanied by dimerization. The enzyme is a glycoprotein. It is stable in presence of non-ionic detergents and can be freeze-dried. The enzyme clots milk at pH 5.5 and has trypsinogen kinase activity. Among several purified proteins that have been tested as a substrate, only horse ferritin was resistant to proteolysis, while myeloma proteins of the A1- and A2-type were readily cleaved, as were two proteinase inhibitors of human serum. Antibodies against purified enzyme did not react with several commercial Candida antigen preparations; antibodies against the enzyme, though, have been detected repeatedly in sera from patients with manifest candidiasis.