Changes in the restriction of molecular rotational diffusion of water-soluble spin labels during fatty acid starvation of yeast.

Yeast mutants lacking fatty acid synthetase activity (fas-) die when deprived of saturated fatty acid under conditions which are otherwise growth-supporting. The spin label technique is used to show that restriction of molecular rotational diffusion of spin label molecules dissolved in aqueous zones increases several fold under conditions of fatty acid starvation while the apparent physical state of cellular hydrocarbon zones remains essentially unchanged. We focus attention on the cellular aqueous interior as the potential site of alteration under selective starvation conditions. Correspondences exist between restriction of molecular motion of water soluble spin labels dissolved in the cell and loss of cell viability. The correspondences to changes in the molecular motion of hydrocarbon soluble spin labels are much less or are not detectable.