Extracellular aspartic proteinases have been implicated for some time as virulence factors associated with Candida opportunistic fungal infections. Our present knowledge of the enzymatic properties of these proteinases is rather limited. Information on their substrate specificity is important for understanding their roles in invasive Candida infections. We have isolated aspartic proteinases from each of the three Candida yeasts, Candida albicans, Candida tropicalis, and Candida parapsilosis, and investigated the specificities of these proteinases using a library of synthetic substrates and testing inhibition by pepstatin A. The specificities of these aspartic proteinases are different from those of major human proteinases, including gastric pepsins, renal renin, and cathepsin D. For the peptide substrate, Lys-Pro-Ala-Leu-Phe*Phe(p-NO2)-Arg-Leu, the values of kcat/Km were 2.95 x 10(6) M-1 s-1 for cleavage by Candida albicans proteinase, 1.60 x 10(6) M-1 s-1 for cleavage by Candida tropicalis proteinase, and 0.59 x 10(6) M-1 s-1 for Candida parapsilosis proteinase. Substantial differences in specificity among the Candida yeast proteinases were identified. For example, Candida tropicalis shows large changes in the kcat/Km value depending on the acidobasic character of the residue occupying the P2 position (1.6 x 10(6) M-1 s-1 for Leu, 0.47 x 10(6) M-1 s-1 for Lys, and 0.05 x 10(6) M-1 s-1 for Asp at P2, respectively). Candida parapsilosis by comparison is tolerant of these substitutions at P2 and is highly restrictive at position P4.(ABSTRACT TRUNCATED AT 250 WORDS)