Lipid hydrogenation induces elevated 18:1-CoA desaturase activity in Candida lipolytica microsomes

Microsomal membranes prepared from the mesophilic yeast Candida lipolytica grown at 10 degrees C were hydrogenated by the homogeneous Pd-catalyst, palladium di (sodium alizarine sulfonate) (Pd(QS)2). After hydrogenation to various levels, the microsomes were washed free of the Pd-complex and transferred to a reaction mixture (containing NADH, MgCl2, ATP, CoA and [14C]18:1-CoA) for assay of 18:1-CoA desaturase activity. Microviscosity alterations were also followed by measuring changes in DPH fluorescence polarization. Rapid catalytic hydrogenation of unsaturated fatty acids of the lipids occurred within 20-120 s, resulting in large increases in 16:0, 18:0 and 18:1 acids and decreases in 18:2 acid. In the range 7-20% 18:0 content, a pronounced increase in desaturase activity was observed, with a maximum of greater than 2-fold at a 18:0 content of 12%, followed by a decrease to the initial activity at 33% 18:0 content. These changes were well-correlated with changes in microviscosity, maximal desaturase activity occurring in the DPH fluorescence anisotropy range of 0.23-0.24; above and below this range, desaturase activities were close to the initial control values. It is suggested that the hydrogenation-induced increase in the formation of 18:2 from 18:1-CoA (proceeding partly through direct desaturation of PC) may be due to changes in conformation of the membrane-bound desaturase enzyme complex as a result of controlled rigidification of the surrounding lipids. The operation of such a self-regulating control mechanism would be consistent with a previously proposed model for microsomal desaturase action.