Nervonic acid biosynthesis by erucyl-CoA elongation in normal and quaking mouse brain microsomes. Elongation of other unsaturated fatty acyl-CoAs (mono and poly-unsaturated)

Abstract

Biosynthesis of nervonic acid by enzymatic elongation of erucyl-CoA has been studied in mouse brain microsomes. The substrate and cofactor requirements have been measured. Malonyl-CoA and reduced nicotine-adenine-dinucleotide phosphate are required, but not FMN, FAD or NADH. The effect of protein concentration, incubation time, ATP and CoA has been determined; the reaction products were checked by gas-liquid chromatography with automatic counting of the eluate. Very little activity was found in hydroxylated fatty acids. In the presence of phosphotransacetylase (which impedes the de novo microsomal system), the main reaction product was nervonic acid. It is concluded that nervonic acid is biosynthesised by elongation using a two-carbon unit from malonyl-CoA. The same enzyme biosynthesises saturated and mono-unsaturated very long chain fatty acids. The elongation capacity of "quaking" microsomes is reduced to 30% of the normal value with both erucyl-CoA and behenyl-CoA. Elongation of trans isomer (brassidyl-CoA) and poly-unsaturated homologue (clupanodonyl-CoA) was compared to elongation of erucyl-CoA in both normal and mutant mice. Both unsaturated acyl-CoAs are elongated under the same conditions as erucyl-CoA in brain: the poly-unsaturated acyl-CoA is elongated more actively than the mono-unsaturated acyl-CoA in the mutant.