Concentrations in vitro of various enzymes in liver homogenates during the first few days of a period of starvation

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Abstract
The activities of some enzymes connected with hepatic glycogen metabolism were measured in rat livers to find an explanation for the increase of glycogen content during starvation after a 6 days' carbohydrate-rich diet as well as after a 6 days' fat-rich diet. Tn the initial phase of the starvation period we noticed strikingly higher activities of several enzymes (phosphorylase, glucokinase) after a carbohydrate-rich diet than after a fat-rich diet. After a carbohydrate-rich diet a decrease in these enzyme activities was noticed during the first 3 days of starvation; from the fourth day of the starvation period onwards enzyme activities were about identical in both groups of animals. Thus, metabolism has adapted after three days of starvation. No clear-cut relationship was observed between (a) enzyme activities of glycogen-degrading and glycogen-synthesizing enzymes and (b) hepatic glycogen accumulation. Comparison of the measured activities of phosphorylase and glucose-6-phosphatase with the activities of glycogen-synthetase, hexokinase, and glucokinase shows that, in vitro, the activity of glycogen-degrading enzymes is always higher than the activity of glycogen-synthesizing enzymes. Thus, glycogen accumulation in the liver during starvation cannot be caused only by changes in the activities of the enzymes due to induction and degradation. Therefore, activation and inactivation or inhibition of enzymes must be very important in the regulation of glycogen synthesis during starvation.

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