Control of Rat Adipose Tissue Hexokinase Isoenzymes by Sugars during in Vitro Incubation

Abstract

Substrate control of HK[hexose kinase]-II activity was studied in rat adipose tissue incubated in vitro for 18 h in a modified TC-199 medium. In addition to glucose, metabolizable substrates of the enzyme, fructose and mannose, maintained higher levels of HK-II than did control incubations. 2DG [2-deoxyglucose] and xylose, both nonmetabolizable sugars which compete with glucose for binding to HK, decreased enzyme activity. Hexoses which do not bind to the active site of the enzyme 3OMG [3-O-methoxyglucose] and galactose, had minimal effect on enzyme activity. Nonhexose energy sources did not maintain high HK-II activity. G-6-P, the product of glucose phosphorylation by HK, increased HK-II despite its minimal transport into the cell. G-6-P may mediate effects of sugars and insulin on HK-II.