Phospholipid synthesizing enzymes of dermatophytes: II. Characterization of choline kinase

Choline kinase was located in the cytosolic fractions of the filamentous, pathogenic fungi, Microsporum gypseum and Epidermophyton floccosum. A broad pH optima (6.0-9.0) was observed for the M. gypseum enzyme, but the E. floccosum enzyme was active at pH 8.4 as well as 10.5, the activity being higher at pH 8.4. Enzyme from both dermatophytes had Km value of 3.3×10^-4 M for choline; however, for ATP, it was 6.6×10^-4 M and 12.6×10^-4 M for M gypseum and E. floccosum, respectively. Choline kinase of both dermatophytes showed SH-group requirement. The M. gypseum choline kinase was inhibited to a greater extent by Mn²⁺, Ca²⁺ and Ba²⁺ than was the E. floccosum enzyme. In comparison to other nucleotides, ATP was the most effective phosphate donor for phosphorylating choline in both dermatophytes. Higher concentrations of ATP inhibited the enzyme in M. gypseum as well as E. floccosum. Phosphorylcholine inhibited the choline kinase activity from both fungi, whereas phosphoethanolamine and glycerol 3-phosphate were stimulatory.