摘要：

Entamoeba histolytica grown in a glucose-containing medium is relatively rich in soluble glucokinase. A method for the visualization of glucokinase activity following electrophoresis on cellulose acetate strips revealed that each of nine strains of typical E. histolytica yielded the same two electrophoretically distinct isoenzymes. Two strains of atypical E. histolytica displayed only a fast-migrating glucokinase which was also characteristic of Entamoeba moshkovskii. Two strains of Entamoeba invadens each gave a single glucokinase band migrating more slowly than the isoenzymes from E. histolytica. The electrophoretic behavior of glucokinase provides a means of characterizing typical E. histolytica and distinguishing it from closely related organisms which may not be human pathogens. Comparative kinetic studies were made on the two glucokinase isoenzymes from a typical E. histolytica. The kinetic properties were, in most respects, indistinguishable. Comparative kinetic studies were made on crude glucokinase from seven typical strains of E. histolytica. All had identical kinetic properties. These properties, determined at pH 7.0 in phosphate buffer, were: apparent Km for glucose, 4 × 10-5 M; for adenosine triphosphate (ATP), 2 × 10-4 M. Apparent Ki's competitive with glucose: N-acetyl-D-glucosamine, 5 × 10-5 M; D-glucosamine, 2 × 10-4 M; and D-xylose, 2.4 × 10-3 M. Apparent Ki competitive with ATP: adenosine monophosphate (AMP), 7 × 10-6 M. Substrates were D-glucose, D-mannose, 2-deoxy-D-glucose, N-acetyl-D-glucosamine, and D-glucosamine, the last four being phosphorylated at 27-42 % the rate of glucose in millimolar concentration. D-Fructose was not a substrate. ATP was the preferred phosphate donor; guanosine triphosphate (GTP), inosine triphosphate (ITP), and uridine triphosphate (UTP) were relatively ineffective. Adenosine diphosphate (ADP), guanosine monophosphate (GMP), and inosine monophosphate (IMP) were competitive inhibitors for ATP, but with Ki's at least fivefold greater than that of AMP. The strong inhibition of amebal glucokinase by AMP was confirmed with an enzyme preparation essentially free from adenylate kinase.

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