Regulatory mechanisms of fatty acid isomers on adenylate cyclase activity from Ceratitis capitata brain.

The regulatory properties of saturated and unsaturated fatty acids on membrane-bound preparations of adenylate cyclase from Ceratitis capitata brains have been investigated. Saturated long-chain fatty acids do not exhibit any significant modification of the enzyme activity of the enzyme preparations but the presence of one, two or three double bonds in the 18C chain provokes an inhibitory effect. Binding of oleate and linoleate to the membrane enzyme preparation is non-specific and simply stoichiometric in the range of concentrations examined. Studies of cis and trans isomers of the double-bond isomers, 18:1(n-9) and 18:1(n-11), reveal the higher inhibitory effect of the cis isomers on membrane-bound adenylate cyclase of the insect brain. The inhibitory effect of cis-vaccinate in the basal conditions of the enzyme assay is identical to the effects obtained in the presence of GTP and octopamine. Insect membrane preparations were labeled with 1,6-diphenyl-1,3,5-hexatriene as fluorescent probe and treated with cis and trans 18:1(n-9) and 18:1(n-11). The fluorescence polarization parameter was measured, from which the microviscosity of the preparations was calculated; microviscosity of the membranes treated with both cis isomers decreased in a clear extent whereas it is not influenced by the trans isomers.