Transport and phosphorylation of sugars in adipose tissue

Publisher Website
Google Scholar
Abstract
Phosphorylation of glucose, mannose and fructose by homogenates of rat-epididymal adipose tissue is carried out by a hexokinase. Its substrate specificity is broadly similar to that of brain hexokinase, although it can phosphorylate mannose and 2-deoxyglucose faster than glucose. The enzyme is inhibited by glucose-6-phosphate and ADP. Mannose phosphate-isomerase activity has also been identified in adipose tissue. In contrast with the glucose phosphate isomerase it does not appear to be in excess over the hexokinase. The relative efficiencies of utilization of glucose, mannose and fructose by intact tissue do not parallel those of phosphorylation by its hexokinase. Moreover, hexose utilization by intact adipose tissue can be strongly inhibited by certain competitive inhibitors of the hexokinase, especially 2-C-hydroxymethylglucose, but not by N-acetylglucosamine. These results indicate the occurrence in adipose tissue of a stereospecific transport of sugars before their phosphorylation. The relationships between hexokinase content and hexose uptake in various conditions suggest that insulin activates the rate of transport without affecting the hexokinase.