A glucokinase from Saccharomyces cerevisiae

Abstract

An ATP:D-glucose 6-phosphotransferase (EC 2.7.1.2) or glucokinase from Saccharomyces cerevisiae is described. The enzyme has been purified about 100-fold from the crude extracts of a hexokinaseless mutant derived from a haploid strain of S. cerevisiae. The K_m values for glucose and ATP are 28 and 50 µm, respectively. The maximal velocity of this enzyme toward fructose is 0.4% of that of glucose. The enzyme showed a marked heterogeneity when sedimented in a sucrose density gradient, its molecular weight ranging from 144,000 to a value in excess of 200,000. Yeast glucokinase shares a number of properties with yeast hexokinase (EC 2.7.1.1) in the semiconstitutive nature of its synthesis with glucose, its broad pH optima, and inhibition with ADP and N-acetylglucosamine. Its mode of reaction with glucose and ATP, as indicated by initial velocity patterns, appears to be random.