Fatty acid synthetase complex from the insect Ceratitis capitata. Structural studies

Effects of palmitoyl-CoA on the structure-function of the fatty acid synthetase complex from Ceratitis capitata

1. The effects of palmitoyl-CoA on the structure and enzyme activity of the fatty acid synthetase from the insect Ceratitis capitata have been examined. 2. The acyl-CoA derivative increases the helical content of the protein from 45 to 60% and inhibits the enzyme activity of the complex. 3. Bovine serum albumin, calf thymus histone H1 and phospholipids protect the enzyme from the inactivation by palmitoyl-CoA. Phospholipids increase also the ellipticity at 220 nm in the enzyme complex. 4. The results obtained show a non specific character for the inhibition and are interpreted in terms of the detergent properties of the long-chain acyl-CoA derivatives.

Fluorescence studies on the lipoprotein complex of the fatty acid synthetase from the insect Ceratitis capitata

The fatty acid synthetase complex from the insect Ceratitis capitata forms a stable lipoprotein complex. The intrinsic fluorescence of the complex was studied by observing the emission spectra with different excitation wavelengths, both in the native complex and after temperature with sodium cholate and sodium dodecyl sulfate. The excitation spectrum of the native form also was recorded. The fluorescence behavior of the native enzyme showed two families of tryptophan residues. Cholate influenced the fluorescence, suggesting that phospholipids are the conformational support at this level. The two families of fluorescing tryptophan residues were similarly accessible to quenching by acrylamide. Thermal changes in the fluorescence characteristics were observed; warming caused a decrease in the quantum yield as well as a red shift in the emission maximum. The high fluorescence remaining after the thermal transition suggested that the lipid-protein interaction was affected but maintained shielding of the fluorophore by the lipids. Fluorescent probe molecules 1,6-diphenyl-hexa-1,3,5-triene (DPH) and dansylphosphatidylethanolamine (DPE) also were used. DPH uptake was temperature dependent, with a middle point consistent with the thermal conformation transition, indicating that internal lipids are nonrandomly distributed within the complex. DPE uptake did not reach the saturation of the complex, suggesting that its solubilization sites would be located on the lipoprotein surface.