CHARACTERIZATION OF A REGULATED FORM OF PHOSPHOLIPASE-D IN THE YEAST SACCHAROMYCES-CEREVISIAE

Phospholipase D (PLD), which is present in bacterial, plant and animal cells, can serve as an important element of signal-transduction pathways. This study examined the potential role of this enzyme in the regulation of Saccharomyces cerevisiae. An assay in vitro using a fluorescent 1-acyl-2-alkyl glycerophosphocholine as substrate was used to assess PLD activity in yeast cell extracts. A neutral PLD activity is present in membranes prepared from both haploid and diploid yeast cells, as evidenced by the production of phosphatidic acid and phosphatidylbutanol in the presence of butanol. Alcohols, in addition to serving as substrates for transphosphatidylation, stimulate PLD activity. Increased PLD activity is detected in membranes when either haploid or diploid cells are incubated in the presence of a nonfermentable carbon source. Membrane PLD activity increases within 10 min after diploid cells are placed in a sporulation-inducing medium lacking nitrogen and containing a non-fermentable carbon source. The increased activity persists for 2-3 h, and then declines to control values. This response occurs in the presence of cycloheximide, an inhibitor of protein synthesis. These data indicate that PLD activity is present in yeast, and that activation of PLD is an early event in sporulation in this organism.