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9 Glycogen Phosphorylase

Elsevier Inc.
DOI: 10.1016/s1874-6047(08)60434-5
  • Biology


Publisher Summary This chapter reviews the knowledge of the enzymic characteristics of phosphorylase and its regulation. The regulation of this enzyme by phosphorylation is superimposed on the evolutionary earlier control by feedback inhibition (glucose and glucose 6-phosphate) and by the cell's energy charge (inhibition by ATP; activation by AMP and Pi). The molecular structure of the enzyme is reviewed because it is the best delineated of any protein dealt with in this volume, and knowledge of this structure has provided us with at least partial explanations of the effects of phosphorylation and of its control. Substrate-directed controls are described in the chapter; interesting in this regard is the glucose-mediated activation of phosphorylase phosphatase in the liver because of an ancient feedback control operating through allosteric conformational changes, which has been adapted to serve as one of the modern physiological mechanisms for glucose homeostasis.

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