Assimilation of methanol by yeasts, a new approach

Dihydroxyacetone kinase of methanol-assimilating yeasts. II. Partial purification and some properties of dihydroxyacetone kinase from Candida methylica

Dihydroxyacetone kinase (DHAK) from the cell-free extract of methanol-grown Candida methylica was partially purified about 100-fold by a procedure employing streptomycin sulfate fractionation, ammonium sulfate fractionation, negative absorption on Cibacron blue F3G-A sephadex G 200 and DEAE-cellulose column chromatography. The enzyme was stable in 50 mM Tris-HCl buffer pH 7.5 containing 60% glycerol at -18 degrees C. The pH optimum for the activity of DHAK from C. methylica was 7.5. The purified enzyme phosphorylated dihydroxyacetone four times faster than D,L-glyceraldehyde. The apparent MICHAELIS-MENTEN constants for dihydroxyacetone and D,L-glyceraldehyde were 0.011 mM and 0.024 mM. Other C3 compounds including glycerol were not phosphorylated. ITP and UTP were used as phosphate donors with a reaction rate of 11% and 3.1%, respectively, in relation to ATP, whereas the reaction rates of DHAK from C. methylica with CTP or GTP were much lower than 1%. The reaction of DHAK depends upon the presence of divalent cations in the assay. The highest activity was found with Mg2+ ions. The reaction rates with Co2+ or Ca2+ ions were only 57.3% and 30.3%, respectively, in relation to the assay with magnesium ions. Manganese chloride in the assay led to a complete loss of activity.

Dihydroxyacetone kinase of methanol-assimilating yeast. I. Regulation of dihydroxyacetone kinase from Candida methylica in situ

In order to investigate the control behaviour of dihydroxyacetone kinase of methanol-grown Candida methylica under nearly physiological conditions kinetic and regulatory studies were carried out in situ. Yeast cells were made permeable to substrate and reaction products by treatment with Triton X-100. Normal Michaelis-Menten kinetics resulted in dependence upon the dihydroxyacetone concentration, both at the pH optimum of 7.6 and near the physiological pH-value of 6.5. The Km obtained for dihydroxyacetone was 0.02 mM, independent of the pH-value. The plots of dihydroxyacetone kinase activity as a function of the ATP concentration revealed complex kinetic characteristics with plateau regions. The maximum reaction rate was reached only after a lag time both at pH 7.6 and concentrations of ATP higher than 5 mM and at pH 6.5 and concentrations of ATP higher than 1.25 mM. Among a great number of tested metabolites no inhibitors of dihydroxyacetone kinase were found. Dihydroxyacetone kinase activity depending upon energy charge according to Atkinson exhibited curves of the U-type. These results and further data concerning the regulation of other enzymes obtained with C. methylica and other yeasts were the basis to propose a preliminary overall model of fine control of the carbon and energy metabolism of methanol-utilizing yeasts.