Effects of transient anaerobic stress on fatty acid desaturation and electron-transport system in Tetrahymena microsomes

Abstract

A transient anaerobic stress of Tetrahymena pyriformis NT-1 for 1 h resulted in slight decreases of unsaturated fatty acids in overall lipid composition. The rates of incorporation of [ 3H]palmitic acid plus sodium [ 14C]acetate into unsaturated fatty acids (palmitoleate, 16:1 Δ 9; oleate, 18:1 Δ 9; linoleate, 18:2 Δ 9,12; γ-linolenate, 18:3 Δ 6,9,12) were drastically reduced by exposing cells to anaerobic conditions for 1 h (anaerobic cells), and thereafter restored to the original levels at 4 h after subsequent reaeration. Activities of Δ 9- and Δ 12-desaturases (palmitoyl-CoA, stearoyl-CoA, oleoyl-CoA) and the terminal component of the desaturation system (cyanide-sensitive factor) decreased to 25–30% in microsomes from anaerobic cells, compared to those from control and reaerobic cells. Furthermore, changes induced by the anaerobic shock in the activities of microsomal reductases and the content of cytochrome b 5 were observed to behave comparably to changes in activities of fatty acyl-CoA desaturases. During the anaerobic state, the half-lives of microsomal enzyme activities (desaturases, cyanide-sensitive factor, reductases) and cytochrome b 5 content were diminished to 30–50% of those of control microsomes. But the K m values of these enzymes did not differ between microsomes from either anaerobic or control cells. These results suggest that the decreased activities of desaturases during anaerobic stress result principally from the reduction of cyanide-sensitive factor content, which would be caused by its instability and repressed synthesis.