Studies on glycogen synthesis in pigeon liver homogenates. Incorporation of hexose into glycogen

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Abstract
Liver homogenates of avian species, but not of mammals, form glycogen from glucose, mannose, fructose and galactose. Incorporation of labeled glucose, fructose and mannose, but not of labeled galactose, into glycogen is diluted isotopically by un-labeled glucose. Except for fructose, glycogen formation from other substrates by pigeon liver homogenates compares favorably with that from the same substrates in pigeon liver slices. Optimum conditions for glycogen synthesis from glucose by pigeon liver homogenates are medium of incubation, 0.175 M-sucrose-45mM_-potassium chlonde-15 mM-glycylglycine buffer, pH 75. concentration of substrate, 15 mM, concentrationof tissue, less than 120 mg /ml , temperature of incubation, 37-43[degree], atmosphere, O2. Uncouplers of oxidative phosphorylation, Ca2+, EDTA, PP1, 2-deoxyglucose 6-phosphate and micro-somal fraction of rat liver are inhibitory to glycogen synthesis from glucose. Starvation of pigeons for 24 and 48 hr. leads to a slight stimulation of glycogen synthesis in their liver homogenates as compared with fed controls. Pigeon liver homogenates can be separated intosubcellular fractions that on reconstitution can synthesize glycogen All the enzymes of the glycogen pathway except soluble high-Km glucokinase are present in pigeon liver.