Fatty Acid Synthesis in Human Adipose Tissue

The concentration of enzymes required for fatty acid synthesis was considerably less in extracts prepared from human omental adipose tissue than from rat epididymal fat. Overall rates of synthesis as measured by the incorporation of radioactive precursors into fatty acids were also much lower in human adipose tissue. The most striking difference was found with citrate-1,5-14C, human adipose tissue incorporating the compound at a rate less than one-tenth that of rat epididymal fat. This finding was consistent with the virtual absence of the citrate cleavage enzyme in human adipose tissue. By contrast, the activities of pyruvate carboxylase and phosphoenolpyruvate carboxykinase, two enzymes necessary for the synthesis of glyceride glycerol from pyruvate, and the long chain fatty acid activating enzyme (or enzymes) were essentially similar in both human and rat adipose tissues. The results are consistent with the hypothesis that synthesis de novo of fatty acids is not an important physiological function of human adipose tissue.