The metabolism of inositol 1,4,5-trisphosphate [Ins(1,4,5)P3] was examined in yeast cells and germ tubes of Candida albicans. Methods have been developed for analysis of the two key metabolic enzymes, Ins(1,4,5)P3 kinase and phosphatase. ATP-dependent Ins(1,4,5)P3 kinase activity was detected predominantly in the soluble fraction of cell extracts and exhibited a K(m) of approximately 9 μM. The apparent K(m) of Ins(1,4,5)P3 phosphatase for Ins(1,4,5)P3 was approximately 480 μM. The slow rate of dephosphorylation of Ins(1,4,5)P3 to inositol bisphosphate suggests a lower importance of the phosphatase within cells compared to the kinase. Since both yeast cells and germ tubes of C. albicans rapidly phosphorylated Ins(1,4,5)P3 to inositol tetrakisphosphate and inositol penta/hexakisphosphate, it is suggested that Ins(1,4,5)P3 has an important role as a precursor for production of these compounds. A sustained increase in cellular Ins(1,4,5)P3 levels was observed during germ tube formation and, prior to the onset of germination between 1 and 2 h incubation, the Ins(1,4,5)P3 content increased up to eightfold. Transient increases in the level of Ins(1,4,5)P3 were also observed during yeast-like growth of C. albicans. The possible role and relative importance of Ins(1,4,5)P3 as a precursor for inositol polyphosphates and in signal transduction involving Ca2+ release from internal stores is discussed.
- Candida albicans
- Inositol 1,4,5-trisphosphate
- Inositol 1,4,5-trisphosphate kinase and phosphatase
- Signal transduction
- Yeast-hyphal dimorphism