Induction of extracellular proteinase in Candida albicans

Pulse-chase experiments indicated that the extracellular proteinase (EPR) of Candida albicans originates as a 45 kDa precursor protein which is processed to a 43 kDa protein prior to secretion. Secretion was routinely stimulated in EPR induction medium which contains bovine serum albumin (BSA) and glucose. Although EPR was not induced without glucose as a carbon source, EPR secretion was induced without the addition of BSA or other nitrogen sources. Furthermore, it was shown that EPR production was not induced at pH > 6.0, irrespective of the presence of a nitrogen source. This suggests that medium pH may act directly upon EPR induction, and not as a secondary effect of the nitrogen supply from EPR-mediated protein digestion, which exhibited a pH optimum of around pH 3.5. When germ tube induced cells were transferred to EPR induction medium, EPR was not induced. Thus, EPR production and germ tube formation may not be induced by the same conditions. We speculate that EPR production and germ tube formation do not co-operate in the invasive process but play different and separate roles.