Glycogen synthesis in amphibian oocytes: Evidence for an indirect pathway

Abstract

Glycogen is the main end product of glucose metabolism in amphibian oocytes. However, in the first few minutes after [U-14C]glucose microinjection most of the label is found in lactate. The burst of lactate production and the shape of the time curves for the labelling of glucose 6-phosphate, fructose 6-phosphate, glucose 1-phosphate and glycogen suggest a precursor-product relationship of lactate with respect to glycogen and its intermediates. Expansion (by microinjection) of the pool of glycolytic intermediates, such as dihydroxyacetone phosphate, glyceraldehyde 3-phosphate, 3-phosphoglycerate or phosphoenolpyruvate, results in a marked decrease in [U-14C]glucose incorporation into glycogen. After co-injection of doubly labelled glucoses, extensive detritiation (93%) of the glucosyl units of glycogen was observed with [2-3H,U-14C]glucose and partial detritiation with [3-3H,U-14C]glucose (34%) or [5-3H,U-14C]glucose (46%). After injection of [6-3H,U-14C]glucose, a small but significant