Loss of inducible D-galactose transport by baker's yeast after osmotic treatment.

The ability of Saccharomyces cerevisiae to transport D-galactose and related sugars with an axial hydroxyl group at C-4, acquired by induction with D-galactose, was lost either by exposing early exponential-phase cells to an osmotic shock involving incubation in 0.6M NaC1O4, 0.66M sucrose and 1mM histidine and transfer to 5mM Tris-HC1 with 2mM dithiothreitol, or simply by transferring them to distilled water. The total amount of protein thus released was 0.1--0.35 and 0.1 mg per mg dry wt., respectively. The shock fluid contained at least six proteins, among them a galactose-binding component. L-Arabinose transport could not be restored by adding the concentrated shock fluid to depleted cells but cells remained viable after the shock and resynthesized the transport system if incubated in a galactose-containing growth medium.