Characterization of the delta 12 desaturase in the American cockroach, Periplaneta americana: the nature of the substrate.

The cockroach, Periplaneta americana, can convert oleic acid (18:1(n - 9], to linoleic acid, (18:2(n - 6], by a microsomal delta 12 desaturase. Most of the desaturase activity was present in the fat body tissue, with lower activity in the epidermis and no detectable activity in the thorax or gut tissue. In incubations of microsomal preparations from fat body tissues with [1-14C]18:1-CoA, increased amounts of [1-14C]18:2 were found with increasing time and protein concentration. The form of the substrate for the delta 12 desaturase was determined to be 18:1-CoA by comparing activity towards [1-14C]18:1-CoA and [1-14C]18:1 transesterified to phospholipid. Ozonolysis of the 18:2 formed from [1-14C]oleoyl-CoA followed by radio-gas-liquid chromatography gave one labeled peak, 9-oxononanoate, which showed that the product of the delta 12 desaturase is the physiologically important isomer, 18:2(n - 6).