Modification of microsomal lipid composition and electron transport enzyme activities in isovalerate-supplemented cells of novel Tetrahymena ISO.

Tetrahymena ISO cells, which have an unusually high level of iso odd-numbered fatty acids, were grown medium supplemented with various concentrations of isovalerate. There was a marked increase in the total proportion of iso odd-numbered fatty acids in supplemented whole cells (28.9 leads to 70.3%) and microsomes (37.7 leads to 84%), with a corresponding decrease in normal fatty acids, although no significant alteration of phospholipid composition was observed during 11 hr isovalerate-supplementation. Microsomal palmitoyl-CoA and stearoyl-CoA desaturase activities in isovalerate-supplemented cells decreased by 45.7% and 30.6% during 11 hr, respectively. NADH-cytochrome c reductase and NADH-ferricyanide reductase activities as well as the content of cytochrome b560ms, which is similar to mammalian microsomal cytochrome b5, were reduced in microsomes from 11 hr-supplemented cells, whereas NADPH-cytochrome c reductase activity was constant. It is suggested that the alteration of the cross-sectional area of lipid molecules in the bilayer, which results from the replacement of normal fatty acids with iso- 15:0 and iso- 17:1, would result in the decline of palmitoyl- and stearoyl-CoA desaturation in the isovalerate-supplemented cells, in order to maintain membrane fluidity at a functional level.