The extracellular
acid proteinase of Candida albicans was purified from culture filtrates by a single-column chromatographic step. The purity of the
enzyme and its unique antigenic properties were confirmed by
polyacrylamide-gel electrophoresis and by reaction with homologous and heterologous anti-sera. The purified
enzyme (PP), which was a carboxyl
proteinase, contained
mannan as an integral part of the molecule. C. albicans
proteinase was detected in experimental candida kidney lesions by indirect immunoflourescence. Precipitating
antibodies to PP and to cytoplasmic extract (CE) were detected in sera from rabbits with chronic, experimental, systemic candidosis; however
precipitins to PP were not found in sera from infected rabbits in which tissue invasion was prevented by antifungal treatment. In retrospective tests with sera from healthy subjects and from patients with and without proven systemic candidosis a qualitative distinction between true and false-positive
precipitins to PP was not found; however, whereas 72% of sera from proven cases of deep-seated
candida infection had anti-PP titres greater than 4 and greater than or equal to anti-CE titres, these same quantitative criteria were met by only 15% of sera from patients for whom information of a diagnosis of candidosis was not available. The purified
proteinase was therefore a more specific
antigen than the widely used cytoplasmic extract for detection of
antibodies in cases of candidosis.