Temperature effects on the proline transport system of Saccharomyces chevalieri

Abstract

1. 1. The effects of temperature on the operation of a proline transport system in yeast are described. 2. 2. The kinetics of l-proline accumulation are not greatly altered by changes in temperature. 3. 3. The initial velocity of l-proline uptake remains constant up to 120 min when cells are heated at 30°, but decreases sharply after 40 min when cells are heated at 42°. This sudden change was found to occur immediately when cells grown at 20° were heated at 42°. 4. 4. The decrease in the initial rate of l-proline uptake after heating at 42° is only partially reversed when the cells are slowly cooled to 30°. On the other hand, the kinetics of accumulation are little affected. Also, the maximum capacity to accumulate l-proline is practically unaltered after heating at 42°. 5. 5. Cells devoid of their cell wall show a sharp decrease in the initial velocity of uptake when heated even only at 32°. The change may be detected after one minute preincubation at 32°. Thus, the cell wall appears to behave as an insulator. 6. 6. The results are discussed in terms of the hypothesis that a temperature increase primarily causes changes in the liquid-crystalline structure of membrane lipids.