Desaturation of myristoyl-CoA to myristoleoyl-CoA by hen liver microsomal delta(9)-desaturase.

Abstract

The desaturation of myristoyl-CoA to myristoleoyl-CoA was measured in microsomal preparations of hen liver. The desaturation was maximal at pH 7.4. The enzymatic activity was linear with time up to 10 min and proportional to microsomal protein concentrations. The initial velocity was linear with substrate concentrations between 13 and up to 200 microM. A decrease in desaturation activity was observed at substrate concentrations greater than 266 microM. There was an absolute requirement for reduced pyridine nucleotide (NADH), while a maximum activity was observed at a myristoyl-CoA:NADH mole ratio of 1. Competitive inhibition studies of myristoyl-CoA desaturation suggest that the inhibitors, stearyl and oleyl-CoA, were more effective than palmitoyl-CoA. Free CoA did not inhibit the delta(9)-desaturase system. The desaturation of myristoyl-CoA was stimulated by bovine serum albumin and reduced by cytoplasmic proteins. The effect of cytoplasmic proteins on the enzymatic reaction was completely abolished by trypsin digestion and boiling for 30 min. On the basis of these data, it was concluded that 9,10-desaturation of acyl-CoA derivatives containing 14-18 carbon fatty acyl chains is catalyzed by the same enzyme.