Synthesis of arachidonoyl coenzyme a and docosahexaenoyl coenzyme a in synaptic plasma membranes of cerebrum and microsomes of cerebrum, cerebellum, and brain stem of rat brain

Abstract

Synthesis of arachidonoyl CoA and docosahexaenoyl CoA in homogenates and microsomes from cerebrum, cerebellum, and brain stem and in synaptic plasma membranes from cerebrum of control rats and rats undergoing bicuculline‐induced status epilepticus were studied. Arachidonoyl CoA synthesis was 3–5 times higher than docosahexaenoyl CoA in homogenates and microsomes. The synaptic plasma membranes showed only 1.5‐ to 2.5‐fold higher activity. The presence of Triton X‐100 (0.1%) in the incubation medium did not alter the activity of arachidonoyl CoA synthesis but did increase the synthesis of docosahexaenoyl CoA in homogenates, microsomes, and especially in synaptic plasma membranes. The synthesis of these polyenoic fatty acyl CoAs were 4–6 times higher in microsomes than in homogenates. Synaptic plasma membranes exhibited about the same amount of activity as homogenates in the synthesis of docosahexaenoyl CoA, but only half the activity of the latter in arachidonoyl CoA synthesis. The synthesis of arachidonoyl CoA and docosahexaenoyl CoA in cerebral homogenates and microsomes was higher than that of cerebellum and brain stem. The apparent Km values for labeled arachidonic acid (17 μM) and docosahexaenoic acid (12 μM) in synaptic plasma membranes were lower than the values for microsomes isolated from different brain regions. The V_max values were also 4–10 times lower. Microsomes from different regions did not differ in their apparent Km values, but did show variations in apparent V_max values. Cerebellar microsomes showed lower V_max values than the other two regions. The presence of Triton X‐100 caused a significant decrease in the apparent Km values with little change in the V_max values. Bicuculline‐induced seizures did not alter the kinetic properties of arachidonoyl CoA and docosahexaenoyl CoA synthesis, except there was a significant decrease in the apparent Km and V_max values for cerebellar microsomal docosahexaenoyl CoA synthesis. In conclusion, there were marked differences in the activation of polyenoic fatty acids in different parts of the brain and in subcellular fractions. Although bicuculline‐induced convulsions accumulate free polyenoic fatty acids in the brain, no changes were detected when the fatty activation was assayed with exogenous cofactors, except in cerebellum.