Molecular control of membrane properties during temperature acclimation. Membrane fluidity regulation of fatty acid desaturase action?

Further studies on the molecular mechanisms of temperature acclimation have been carried out using the ciliate Tetrahymena pyriformis. The most prominent change in lipid metabolism during acclimation to high temperature--depression of fatty acid desaturase activity--could be simulated by supplementing the growth medium of isothermally-grown cells with polyunsaturated fatty acids. Such cells resisted the membrane-fluidizing effect of the incorporated exogenous acids by increased use of de novo synthesized saturated acids in their phospholipids. The data support the conclusions arising from earlier experiments with temperature-shifted cells (Martin, C.E., Hiramitsu, K., Kitajima, Y., Nozawa, Y., Skriver, L., and Thompson, G.A., Jr. (1976), Biochemistry 15), showing that, when membrane fluidity increased to a superoptimal level, the activity of membrane-associated fatty acid desaturases was decreased. Since the reaction is controlled by membrane fluidity, rather than temperature per se, we postulate that it is the general mechnaism employed by cells adjusting to any fluidity-modifying factor, such as cations, drugs, etc.