Temperature Dependency of the Anomeric Specificity of Yeast and Bovine Hexokinases

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Abstract
The phosphorylation of .alpha.- and .beta.-D-glucose by either yeast hexokinase or beef heart hexokinase was measured at both 10 and 30.degree. C. At 30.degree. C, the anomeric specificity of yeast hexokinase represented a mirror image of that of bovine hexokinase, in terms of both maximal velocity and affinity. A decrease in temperature apparently accentuated the anomeric difference in both maximal velocity and affinity to bovine hexokinase. Such a difference consisted in a higher maximal velocity with .beta.- than .alpha.-D-glucose, but a greater affinity for the .alpha.-than .beta.-anomer. It yeast hexokinase, however, the decrease in temperature suppressed the anomeric difference in maximal velocity and inversed the anomeric difference in affinity. In the case of both enzymes, the fall in temperature decreased more the maximal velocity recorded with .alpha.-D-glucose than that measured with .beta.-D-glucose, and severely lowered the Km for .alpha.-D-glucose, whilst failing to affect significantly the Km for .beta.-D-glucose. These findings, which allow to reconcile prior apparently conflicting data, reveal that the anomeric behaviour of hexokinase is affected by the ambient temperature. Our data also support the view that hexokinase underwent a phylogenic evolution in terms of its anomeric specificity.