Wax ester biosynthesis in a calanoid copepod, Calanus finmarchicus and a fresh-water teleost, Trichogaster trichopterus
The de novo formation of long-chain fatty acids and the reduction of long-chain fatty acids to the corresponding fatty alcohol were studied in the calanoid copepod Calanus finmarchicus (Calanus) and the fresh-water fish, Trichogaster trichopterus (the gourami). De novo biosynthesis of fatty acids by the enzyme fatty acid synthase (FAS) was localised in the 6.3 x 106g-min supernatant ('cytosolic' fraction) of homogenates of whole Calanus and was characteristic of a Type 1 multienzyme complex. The formation of fatty acids required the presence of acetyl-CoA, malonyl-CoA and was specific for NADPH as the reductant. The main products of the reaction were the saturated long-chain fatty acids stearic acid and palmitic acid, accounting for 54% and 25% of the total fatty acid product, respectively. The alcohol-forming enzyme, NADPH-fatty acyl-CoA oxidoreductase, from both Calanus the gourami roe was membrane-associated. Differential ultracentrifugation showed that a 6.3 x 106g-min pellet (the 'particulate' fraction) was most active in the formation of long-chain fatty acohols. The specific activity of the enzyme in the gourami roe particulate fraction was over 100-fold higher than that in the Calanus particulate fraction. Both systems required the presence of an acyl-CoA generating system in the form of exogenous CoASH, ATP and Mg++. The reaction was specific for NADPH as the reductant in the case of the gourami roe system. However, NADH substituted for NADPH in the Calanus system. Palmitic acid, in the presence of an acyl-CoA generating system, was the most effective substrate with the 18:0, 18:1 and 22:1 substrates giving progressively lower activities.