Description: Recently, three distinct isoforms of phospholipase D (PLD) were identified in Arabidopsis thaliana. PLD α represents the well-known form found in plants, while PLD β and γ have been only recently discovered (Pappan et al., 1997b; Qin et al., 1997). These isoforms differ in substrate selectivity and cofactors required for activity. Here, I report that PLD β and γ isoforms were active toward N-acylphosphatidylethanolamine (NAPE), but PLD α was not. The ability of PLD β and γ to hydrolyze NAPE marks a key difference from PLD α. N-acylethanolamines (NAE), the hydrolytic products of NAPE by PLD β and γ, inhibited PLD α from castor bean and cabbage. Inhibition of PLD α by NAE was dose-dependent and inversely proportional to acyl chain length and degree of unsaturation. Enzyme kinetic analysis suggested non-competitive inhibition of PLD α by NAE 14:0. In addition, a 1.2-kb tobacco (Nicotiana tabacum L.) cDNA fragment was isolated that possessed a 74% amino acid identity to Arabidopsis PLD β indicating that this isoform is expressed in tobacco cells. Collectively, these results provide evidence for NAE producing PLD activities and suggest a possible regulatory role for NAE with respect to PLD α.
Date: December 1998
Creator: Brown, Shea Austin