The Determination of Chitin Synthases by Varying pH and Divalent Cations in Candida albicans

The Chsl, Chs2, and Chs3 activities of a pathogenic fungus, Candida albicans, perform the same biochemical reactions, but exert different functions. Therefore, the determination of each enzyme activity is important. The three chitin synthases differ in their optimal pH and the effect of divalent cations as either stimulatory or inhibitory factors. The CAChsl, CAChs2, and CAChs3 activities are optimal at pH 7.5, 6.5, and 8.5, respectively. $Co^{2+} stimulates CAChsl and CAChs3, but inhibits CAChs2. $Ni^{2＋}$ inhibits CAChsl and CAChs2 with little effect on CAChs3. $Mg^{2＋}$ stimulates CAChs2 and CAChs3, but hardly affects CAChsl. These characteristics are similar to those of the Saccharomyces cerevisiae enzymes except in degree. The sensitivity against $Ni^{2＋}$ of CAChsl is higher than that of CAChs2, whereas the reverse is true in S. cerevisiae. Metal dependence of chitin synthases in C. albicans is less marked than that in S. cerevisiae, except for CAChs2. The activities of CAChsl and CAChs3 from EDTA-treated membranes were increased 1.5 fold, while that of CAChs2 was stimulated 7 fold in the presence of divalent cations. These results could provide new criteria for screening systems of antifungal agents.