Glucose formation by the 27,500 g supernatant fraction of rat liver homogenate

Abstract

The gluconeogenic properties of the 27,500 g supernatant fraction of a 20% rat liver homogenate were investigated. This cell-free system, prepared from a salt solution simulating the ionic composition of intracellular fluid, was found to be capable of forming glucose from added glucose 6-phosphate, fructose 6-phosphate, fructose 1,6-diphosphate, and dihydroxyacetone phosphate. No metabolism of l-α-glycerophosphate occurred. Fructose 1,6-diphosphate and dihydroxyacetone phosphate were metabolized also in the direction of glycolysis; 3-phosphoglycerate was metabolized exclusively in this direction. Inhibition of the enolase reaction with NaF prevented metabolism of 3-phosphoglycerate unless both ATP and NADH were added to the system, in which case l-α-glycerophosphate was formed. The addition of ATP and NADH to the system in the absence of NaF resulted in the formation of both lactate and l-α-glycerophosphate from 3-phosphoglycerate. The conversion of fructose 1,6-diphosphate and fructose 6-phosphate to glucose was effectively prevented by the addition of ATP to the system, which caused it to metabolize these substrates by glycolysis.