Phosphatidylcholine is essential for efficient functioning of the mitochondrial glycerol-3-phosphate dehydrogenase Gut2 in Saccharomyces cerevisiae

Gut2, the mitochondrial glycerol-3-phosphate dehydrogenase, was previously shown to become preferentially labelled with photoactivatable phosphatidylcholine (PC), pointing to a functional relation between these molecules. In the present study we analyzed whether Gut2 functioning depends on the PC content of yeast cells, using PC biosynthetic mutants in which the PC content was lowered. PC depletion was found to reduce growth on glycerol and to increase glycerol excretion, both indicating that PC is needed for optimal Gut2 functioning in vivo. Using several in vitro approaches the nature of the dependence of Gut2 functioning on cellular PC contents was investigated. The results of these experiments suggest that it is unlikely that the effects observed in vivo are due to changes in cellular Gut2 content, in specific activity of Gut2 in isolated mitochondria, or in the membrane association of Gut2, upon lowering the PC level. The in vivo effects are more likely an indirect result of PC depletion-induced changes in the cellular context in which Gut2 functions, that are not manifested in the in vitro systems used.