Journal of Lipid Research, Vol. 5, 548-553, October 1964
Copyright © 1964 by Lipid Research, Inc.

Conversion of glutamate carbon to fatty acid carbon via citrate in rat epididymal fat pads

J. Madsen , S. Abraham , and I. L. Chaikoff

Department of Physiology, University of California, Berkeley, California

The incorporation of the C¹⁴ of glutamate-2-C¹⁴ and glutamate-5-C¹⁴ into fatty acids by epididymal fat pads and liver slices suggests the operation of the following metabolic pathway: -ketoglutarate isocitrate cis-aconitate citrate acetyl CoA + oxalacetate (referred to as the backward reaction of the Krebs cycle).

Fatty acid-C¹⁴ recoveries from glutamate-2-C¹⁴, glutamate-5-C¹⁴, and acetate-1-C¹⁴ in experiments with epididymal fat pads from rats fed a stock diet were increased by the addition of glucose to the incubation medium, and further increased by in vitro addition of insulin. From these experiments it was calculated that, of the total amount of glutamate metabolized via the Krebs cycle, 6% proceeded by way of the backward reaction in the absence of glucose, 17% in the presence of glucose, and 35% when both glucose and insulin were added to the incubation medium. Fatty acid-C¹⁴ yields from glutamate-5-C¹⁴ and acetate-1-C¹⁴ were highest when the epididymal fat was taken from rats that had been fasted and then refed a 60% glucose diet. The in vitro addition of glucose or glucose plus insulin to the latter type of fat pad had no appreciable effect on the fatty acid-C¹⁴ yields.

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