Mechanism and specificity of formation of long chain alcohols by developing rat brain.

The enzymatic reduction of acyl-CoA to long chain alcohol by NADPH ion a particulate fraction from developing rat brain has been studied in detail. Addition of serum album in to the assay stimulated activity, due to protection of the substrate acyl-CoA from hydrolysis by an endogenous hydrolase. The optimum amount of albumin depended upon the amount of acyl-CoA added and was found to be 0.5 to 2.0 mol of albumin/mol of acyl-CoA. A series of saturated and unsaturated acyl-CoAs from C12 to C22 was tested, and it was found that the enzyme was specific for only the palmitoyl (16:0)-, stearoyl (18:0)-, and oleoyl (18:1)-CoAs, thus accounting for the observed ether lipid composition in brain. The enzyme specifically utilized only B side hydrogen of [4-3H]NADPH (2 mol/mol of alcohol formed). By various criteria, it was shown that free palmitaldehyde was not an intermediate of the reaction, implying that a single enzyme catalyzes the two consecutive reductions. However, small amounts of palmitaldehyde were produced by this system and were shown to be derived from the same enzyme; probably resulting from partial degradation of an unstable enzyme-bound intermediate. Activity was fully inhibited by sulfhydryl reagents, and from the results of substrate protection experiments, it was concluded that an essential thiol was located at the active site of the enzyme.