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Regulation of Gluconeogenesis at Phosphoenolpyruvate Carboxykinase

1984; Academic Press; Linguagem: Inglês

10.1016/b978-0-12-152824-9.50023-x

0070-2137

Henry A. Lardy, Peter Hughes,

Ion channel regulation and function

This chapter discusses the regulation of gluconeogenesis at phosphoenolpyruvate carboxykinase. It describes the formation of phosphoenolpyruvate (P-enolpyruvate) from oxalacetate. P-enolpyruvate carboxy-kinase (PEPCK) has only a single known function but it exists in two isozyme forms in two different cellular locations and its activity is controlled in multiple modes. It is the first enzyme in the gluconeogenic sequence that functions solely in glucose formation and not in other major metabolic pathways. The catalytic activity of the cytosolic PEPCK is influenced by the redox state of its thiols, by the presence or absence of certain divalent transition metal ions, and by certain factors that permit ferrous ion to activate the enzyme. These are called ferroactivators and their production is regulated by events that alter the rates of glucose synthesis. A role for ferrous ion in stimulating this enzyme was discovered when it was found that tryptophan administered to rats caused gluconeogenesis to be inhibited at the site of PEPCK but greatly increased the assayable activity of this enzyme in liver cytosol. Although Mn2+, Co2+, and Cd2+ stimulate cytosolic PEPCK activity, it is believed that the evidence indicates that Fe2+ is the most important physiological activator.