The effect of 3-mercaptopicolinic acid and substrate interactions on the incorporation of lipogenic precursors into glyceride-glycerol, glyceride-fatty acids and nonesterified fatty acids in bovine adipose tissue.

The effects of 3-mercaptopicolinic acid, an inhibitor of phosphoenolpyruvate carboxykinase, were studied in bovine subcutaneous adipose tissue slices in vitro. Lactate and glucose stimulated the incorporation of [U-14C]acetate into total lipids and nonesterified fatty acids. 3-Mercaptopicolinic acid abolished the stimulatory effect of lactate on total synthesis but had no effect on that from glucose. The inhibitor decreased glyceride-glycerol and glyceride-fatty acid synthesis from L-[U-14C]lactate by 90 and 30%, respectively; glyceride-glycerol synthesis from D-[U-14C]glucose was refractory to inhibition by 3-mercaptopicolinic acid, whereas the inhibitor tended to increase glyceride-fatty acid synthesis from glucose. The presence of lactate plus glucose in the incubation media elicited a greater than additive stimulation of acetate incorporation into total lipids. Glucose doubled the incorporation of lactate into glyceride-fatty acids, but had no effect on the net incorporation of lactate into nonesterified fatty acids. Lactate, but not glucose, stimulated the incorporation of [1-14C]palmitate into glyceride-fatty acids; 3-mercaptopicolinic acid increased this rate for all substrate combinations studied, although this was opposite to expected results. As determined with 3H2O, lactate and glucose stimulated the synthesis of total lipids, and 3-mercaptopicolinic acid decreased the stimulatory effects of lactate and glucose on 3H2O incorporation. The results suggest that lactate, and possibly glucose, stimulate the incorporation of acetate into fatty acids by increasing the availability of alpha-glycerophosphate.