D-Glucose is phosphorylated by glucokinase and three tissue-specific hexokinases to produce glucose-6-phosphate in humans. D-Mannoheptulose is a heptose that inhibits glucokinases and hexokinases from diverse organisms through competition with D-glucose (Ki = 0.25 mM). It blocks glucose oxidation and glucose-mediated insulin release from pancreatic islet cells. D-Mannoheptulose prevents the conversion of glucose to glucose-6-phosphate that can mediate the activation of the carbohydrate response element binding protein. By blocking glucose phosphorylation, D-mannoheptulose causes transient hyperglycemia in dogs when given at 1 g/kg but not at 8 mg/kg, although postprandial energy expenditure is increased at the lower dose.