Studies on the Active Site of Yeast Hexokinase. Specific Phosphorylation of a Serine Residue Induced by d-Xylose and ATPMg

Abstract

Yeast hexokinase A (ATP: d-hexose 6-phosphotransterase) is inactivated when incubated in the presence of xylose and ATPMg, or in the presence of d-lyxose in a reaction medium in which ATPMg is being continuously regenerated (phosphoeno/pyruvate and pyruvate kinase). The inactivation is due to the phosphorylation of the protein. A linear relationship was observed between the inactivation and the incorporation of 32P from [y-32P]ATP. All hexokinase and ATPase activity of the enzyme is lost when one phosphoryl group is incorporated per enzyme subunit (molecular weight 51000). The phosphoryl group is covalently bound by a ester linkage with a serine residue of the protein.