Abstract
Rat kidney cortex microsomal preparations were unable to catalyze Δ9, Δ6, and Δ5 desaturation of stearoylcoenzyme A (CoA), linoleoyl‐CoA and dihomo‐γ‐linolenoyl‐CoA, respectively. The kidney cortex microsomal fraction, however, did catalyze the malonyl‐CoA dependent fatty acyl‐CoA elongation. The biochemical properties of palmitoyl‐CoA elongation were studied as a function of protein concentration, time, reduced nicotinamide adenine dinucleotide phosphate (NADPH), malonyl‐CoA and substrate concentrations; of the substrates investigated, Δ6.9.12–18∶3 was the most active. Unlike what was observed in the hepatic system, a high‐carbohydrate, fat‐free diet did not induced kidney fatty acid chain elongation. All intermediate kidney cortex microsomal reactions,i.e., β‐ketoacyl‐CoA reductase, β‐hydroxyacyl‐CoA dehydrase andtrans‐2‐enoyl‐CoA reductase activities, were significantly higher (greater than one order of magnitude) than the condensing enzyme activity, suggesting that the rate‐limiting step in total elongation is the initial condensation reaction. Contrary to other reports, the results suggest that the kidney cannot synthesize arachidonic acid needed for eicosanoid production.