Conversion of Glutamate Carbon to Fatty Acid Carbon via Citrate in Rat Epididymal Fat Pads.

The incorporation of the C14 of glutamate-2-CI4 and glutamate-5-C14 into fatty acids by epididymal fat pads and liver slices suggests the operation of the following metabolic pathway : a-ketoglutarate + isocitrate -+ cbaconitate + citrate + acetyl CoA + oxalacetate (referred to as the backward reaction of the Krebs cycle). Fatty acid-C14 recoveries from glutamate-2-C14, glutamate5-C14, and acetate-l-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-C1* yields from glutamate5-W and acetate-1 -C14 were highest when the epididymal fat was taken from rats that had been fasted and then refed a 60y0 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.