Formation of Monoenoic Fatty Acids by Desaturation in Rat Brain Homogenate SOME PROPERTIES OF THE ENZYlLIE SYSTFXI OF IO-DAY-OLD RRAIr\‘*

Desaturation of [1-r4C]stearic acid, [lJ4C]palmitic acid, and [l-14C]stearoyl-CoA was measured in homogenates of lo-day-old rat brain. Desaturation was maximal with stearoyl-CoA at pH 6.0 to 6.6. With free fatty acids, monoene formation was maximal at pH 7.2 to 7.6; stearic acid was more actively desaturated than palmitic acid. Activity with stearic acid or stearoyl-CoA was linear with protein concentration of 2 to 6 mg per ml and time to 10 min and was optimal at 37 to 45”. At pH 7.4, fatty acid desaturation was not limited by the formation of fatty acyl-CoA derivatives when coenzyme A, Mg?+, and ATP were added. Rapid loss of activity in vitro prevented accurate subcellular location of the enzyme system. Oxygen and NAD+ or NADH were necessary for maximal activity. Diphosphonucleotides were more active than triphosphonucleotides, and oxidized were as effective as reduced forms. The monoene fraction from desaturation of the labeled stearic acid was 91% oleic acid (lS:l(n-9)); desaturation of palmitic acid produced 22% palmitoleic acid (16: l(n-7)) and 72% cis-vaccenic acid (18: l(n-7)). At concentrations approximating normal tissue evels, these monoenes did not inhibit desaturation.