Glycogen synthesis by the direct or indirect pathways depends on glucose availability: In vivo studies in frog oocytes

Abstract

Abstract Besides the classic direct route, frog oocytes incorporate glucosyl units into glycogen by the so-called indirect pathway. The operation of both pathways depends on glucose availability. Below 0.5 mM glucose (calculated intracellular concentration), the indirect route accounts for 90% of polysaccharide formation, while the direct pathway supports 70% of total glucose incorporation when administered glucose is above 1.5 mM. A sigmoidal curve was obtained for the direct pathway with nH = 2.04, and half saturation was reached at 2.6 mM glucose. The curve for the indirect route presented an nH of 1.15 and an S0.5 of 0.9 mM glucose.