Enzyme site-specific changes in hepatic microsomal fatty acid chain elongation in streptozotocin-induced diabetic rats

The hepatic microsomal fatty acid chain elongation of palmitoyl-CoA and γ-linolenoyl-CoA was diminished by 40–50% in male Sprague-Dawley rats made diabetic for 2 and 4 weeks following the intravenous administration of a single dose (65 mg/kg) of streptozotocin. Analysis of the activities of the four enzymatic components showed that only one enzyme, the condensing enzyme, which catalyzes the initial and rate-limiting step in chain elongation, was altered by the diabetic state. Both chain elongation and condensation activities were depressed to the same extent, whereas β-ketoacyl-CoA reductase, β-hydroxyacyl-CoA dehydrase and trans-2-enoyl-CoA reductase activities were the same as the values obtained with non-diabetic controls. 2 week administration of 10 units of insulin per day to rats which were diabetic for a 2-week period resulted in the reversal of the reduced palmitoyl-CoA elongation and condensation activities to control values. However, neither the condensation nor the elongation of γ-linolenoyl was reversed by the insulin treatment. These results support the notion of multiple condensing enzymes or chain elongation systems.