Regulation of chitin synthesis during germ-tube formation in Candida albicans.

The synthesis of chitin during germ-tube formation in Candida albicans may be regulated by the first and last steps in the chitin pathway: namely L-glutamine-D-fructose-6-phosphate aminotransferase and chitin synthase. Induction of germ-tube formation with either glucose and glutamine or serum was accompanied by a 4-fold increase in the specific activity of the aminotransferase. Chitin synthase in C. albicans is synthesized as a proenzyme. N-acetyl glucosamine increased the enzymic activity of the activated enzyme 3-fold and the enzyme exhibited positive co-operativity with the substrate. UDP-N-acetylglucosamine. Although chitin synthase was inhibited by polyoxin D (Ki = 1.2 microM) this antibiotic did not affect germination. During germ-tube formation the total chitin synthase activity increased 1.4-fold and the expressed activity (in vivo activated proenxyme) increased 5-fold. These results could account for the reported 5-fold increase in chitin content observed during the yeast to mycelial transformation.