Effects of sterol manipulation on microsomal desaturase activities in Tetrahymena: with regard to thermal acclimation.

There was a great increase in microsomal palmitoyl-CoA desaturase activity of ergosterol-replaced Tetrahymena (ergosterol-cells), which exhibited a pronounced elevation of palmitoleate (16:1 delta 9) in fatty acid composition. At 2 hr after the growth temperature-shift from 34 to 15 degrees C (shift-down), palmitoyl-CoA desaturase activity in ergosterol-cells increased 6-fold compared to that in native cells containing tetrahymanol before the shift-down. These results suggest that, unlike drastic increases of palmitoyl-CoA, stearoyl-CoA and oleoyl-CoA desaturase activities by the shift-down in native cells, ergosterol-cells accomplish an adaptive modification of fatty acid composition by a preferential increase in palmitoyl-CoA desaturase activity, being which is principally due to the increased content of the terminal component (cyanide sensitive factor; CSF) of the desaturase system.