Paths of carbon in gluconeogenesis and lipogenesis: the role of mitochondria in supplying precursors of phosphoenolpyruvate.

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Abstract
Gluconeogenesis in rat liver involves carboxylation of pyruvate to oxalacetate in mito-chondria. Oxalacetate does not diffuse from the mitochondria but is transaminated to form aspartate or reduced to malate. Aspartate, malate, [alpha]-ketoglutarate, and some citrate diffuse from mitochondria. In the extramitochondrial compartment of the cell, oxidation of malate and transamination of aspartate yield oxalacetate which can be converted to phosphoenolpyruvate by the soluble carboxykinase. The production, in mitochondria, of a variety of compounds that may serve as precursors of phosphoenolpyruvate in the extramitochondrial compartment provides a multiplicity of sites for metabolic controls.