Dihydroxyacetone Synthase: a Special Transketolase for Formaldehyde Fixation from the Methylotrophic Yeast Candida boidinii CBS 5777

Abstract

SUMMARY: The transketolase synthesized by Candida boidinii CBS 5777 during growth on non-C1 substrates has been purified and shown to have a molecular weight of approximately 135000 and to consist of two subunits of approximate molecular weight 68000. The enzyme is active with xylulose 5-phosphate as glycolyl donor and ribose 5-phosphate as acceptor; under the conditions of assay formaldehyde was inactive as acceptor. Candida boidinii CBS 5777 also synthesizes a second transketolase during growth on methanol. This enzyme, which is unstable, has been purified to homogeneity. It has a wide substrate specificity towards glycolyl donors and acceptors; formaldehyde is a good acceptor and in terms of its physiological role during growth on methanol the enzyme can be described as a dihydroxyacetone synthase. This enzyme has a molecular weight of 105000-110000, with two subunits of molecular weight 62000-67000. Its properties have been compared with analogous enzymes purified elsewhere from methanol-grown Candida boidinii KD1 and Candida boidinii (Kloeckera sp.) 2201.