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Involvement of hepatocyte membranes in glycogen metabolism
A considerable amount of evidence supports the contention that elements of the endoplasmic reticulum are involved in glycogen metabolism. The present study examined the effects of starvation and glycogen depletion on the membrane elements of rat liver. Membrane elements were isopycnically banded by reorienting gradient zonal centrifugation in sucrose density gradients. Changes in the distribution and density of the various elements were examined during increasing periods of starvation and reflect the structural and physiological changes occurring in the tissue. A remarkable increase in glucose-6- phosphatase activity and protein concentration was observed within a short period of starvation. A membrane fraction corresponding to membrane bound glycogen was found to disappear after 48 hours of starvation. It is proposed that this fraction corresponds to desmo glycogen identified previously. A transitional membrane density stage is reported, and probably represents the intermediate density of rough membranes as ribosomes are removed. Both rough and smooth endoplasmic reticulum increased in density during long-term starvation. This resulted from loss of lipid from both membrane types.