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We developed a host-vector system for transformation and gene cloning experiments using the methylotrophic yeast Hansenula polymorpha. Regeneration of protoplasts in a medium containing polyethylene glycol before plating made transformation more efficient and reproducible (2 to 3 x 10(4) micrograms DNA). The frequency of transformation was significantly lower when dominant resistance marker Cup1r was used for transformant selection. The transformation system developed was used to clone the DNA fragment which complements functionally the defect in the dihydroxyacetone kinase (DHAK*) activity of a H. polymorpha mutant strain. The DNA insert isolated was shown to increase by up to ten times the activity of DHAK in transformants carrying recombinant plasmids. When recombinant plasmids were introduced into S. cerevisiae, the transformants obtained acquired the ability to grow on the medium with dihydroxyacetone as a sole carbon source and the activity of DHAK was observed.

A procedure for purification of dihydroxyacetone synthase catalyzing the formation of dihydroxyacetone and glyceraldehyde 3-phosphate from formaldehyde and xylulose 5-phosphate has been developed. Using ion-exchangers with increasing affinity for dihydroxyacetone synthase, a homogenous preparation of the enzyme with specific activity of 2 u./mg has been obtained. The enzyme is made up of 2 subunits with m. w. of 76,000, contains thiamine pyrophosphate, requires Mg2+ for its activity and differs from yeast transketolase by substrate specificity and some other properties. The role of dihydroxyacetone synthase in metabolism of methanol-utilizing yeasts is discussed.

The activity of enzymes involved in methanol oxidation and assimilation as well as the levels of formaldehyde and glutathione were determined during batch cultivation of Candida boidinii KD1 in a medium with methanol. The distribution of [14C]methanol between oxidative and biosynthetic processes in the yeast was analysed. Changes in the concentrations of formaldehyde and glutathione were found to correlate with the activity of formaldehyde dehydrogenase. The results indicate that an increase in the concentration of reduced glutathione (GSH) at the early logarithmic phase of the yeast growth stimulates formaldehyde oxidation via formate to carbon dioxide whereas a subsequent decrease in the concentration of GSH favours formaldehyde assimilation.

A procedure for isolation of a homogeneous dihydroxyacetone kinase including fractionation by polyethylene glycol and ion-exchange chromatography on polyethylenimine-Biogel has been developed. The enzyme is a dimer with Mr = 139 000 (2.71 000 according to SDS disc electrophoresis) and has a pI of 4.64 and pH optimum of 7.8-8.2. The enzyme phosphorylates dihydroxyacetone and, in a lesser degree, glyceraldehyde. ATP is the most efficient phosphate group donor for the enzyme. When ITP, GTP, CTP and UTP are used, the dihydroxyacetone kinase activity is about 30%.