Abstract
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 Km 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.
Highlights
The enzyme has been purified about loo-fold from the crude extracts of a hexokinaseless mutant derived from a haploid
While studying the properties of 2-deoxyglucoseresistant mutants of Saccharomyces cerevisiae we found that resistance to this sugar analogue does not necessarily confer glucose negativity
The wild type, grows well on glucose or fructose. This was soon traced to the presence of an enzyme t.hat phosphorylates glucose but not fructose
Summary
An ATP:r+glucose 6-phosphotransferase (EC 2.7.1.2) or glucokinase from Saccharomyces cerevisiae is described. The maximal velocity of this enzyme toward fructose is 0.4% of that of glucose. Ilthough specific glucokinases (EC 2.5.1.2) have been described in a number of bacteria [1, 2] ant mammals [3, 4], such an enzyme has not, been described in yeast. While studying the properties of 2-deoxyglucoseresistant mutants of Saccharomyces cerevisiae we found that resistance to this sugar analogue does not necessarily confer glucose negativity. The wild type, grows well on glucose or fructose. This was soon traced to the presence of an enzyme t.hat phosphorylates glucose but not fructose. We describe here the partial purification and the properties of this enzyme from S. cerevisiue
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