Carbon-13 NMR Studies and Purification of Gluconate Pathway Enzymes from Schizosaccharomyces pombe

Evidence is presented to show that D-glucose in Schizosaccharomyces pombe can be metabolized via a new alternative route (gluconate pathway) in addition to the regular D-glucose 6-phosphate route, This gluconate pathway consists of two steps: oxidation of D-glucose to D-gluconate by NADP+-dependent glucose dehydrogenase and phosphorylation of D-gluconate to 6-phosphogluconate by gluconate kinase. The formation of D-gluconate and 6-phosphogluconate from D-glucose was monitored by 13C nuclear magnetic resonance spectroscopy using D-[1-13C]glucose and D-[U-13C]glucose. The operation of the gluconate pathway was further substantiated by the purification of its two member enzymes, glucose dehydrogenase and gluconate kinase, from the cell-free extract of the fission yeast. Glucose dehydrogenase has been purified (580-fold) to homogeneity by the combined procedures of ammonium sulfate fractionation, Sephadex gel filtration, cation-exchange chromatography, matrex gel chromatography, and agarose-NADP+ affinity chromatography. The purified enzyme is monomeric with a relative molecular weight of 6.65 × 104 Da. Gluconate kinase has been purified (410-fold) to near homogeneity by a combination of chromatographic procedures using Biogels, matrex gel, and agarose gels. The purified enzyme is monomeric with a relative molecular weight of 2.4 × 104 Da. The gluconate pathway presented here provides an alternative route for the D-glucose metabolism in Sch. pombe. Meanwhile, this paper documents another metabolic difference between the fission and budding yeasts.