Studies on the biological control of glycogen metabolism in liver. III. Subcellular distribution of glycogen metabolizing enzymes

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Abstract
In a study of the subcellular distribution of the enzymes of the glycogen cycle in rat liver, glycogen synthetase was found in both the microsomal pellet and supernatant fractions, but the activity was always greater in the pellet than in the supernatant fraction. Variations in the concentration of liver glycogen, brought about by fasting and refeeding, did not alter this distribution. In agreement with the results of others, phosphorylase appeared almost entirely in the microsomal fraction, presumably bound to glycogen, when liver glycogen was high, or in the supernatant fraction when liver glycogen was low. These results indicate that synthetase and phosphorylase may be bound with different affinities or to different forms of glycogen.Regardless of whether the animals were fasted or fed, significant amounts of UDPG pyrophosphorylase activity appeared in the microsomal pellet fraction. The remainder of UDPG pyrophosphorylase and all of phosphoglucomutase activities were present in the microsomal supernatant fraction. As synthetase and phosphorylase are bound to glycogen, which in turn is known to be associated with the endoplasmic reticulum, the occurrence of UDPG pyrophosphorylase, synthetase, and phosphorylase in the microsomal fraction may have functional significance to the glycogen cycle.

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