Aluminum fluoride inhibition of cabbage phospholipase D by a phosphate-mimicking mechanism

Aluminum fluoride (AlF4-) inhibited phospholipase D (PLD) purified from cabbage in both PIP2-dependent and PIP2-independent assays, consistent with its previously observed effect on mammalian PLD, The possibility that AlF4- may exert this effect through its known phosphate-mimicking property,vas examined. Inorganic phosphate, as well as two phosphate analogs, beryllium fluoride and orthovanadate, also inhibited cabbage PLD, Enzyme kinetic studies confirmed that PLD followed Hill kinetics, characteristic for allosteric enzymes, with an apparent Hill coefficient (n(app)) of 3.8, indicating positive cooperativity among multiple substrate-binding sites and suggesting possible functional oligomerization of the enzyme. AlF4- modification of PLD kinetics was consistent with a competitive mode of enzyme inhibition. It is therefore proposed that AlF4-, and other phosphate analogs, inhibits plant PLD by competing with a substrate phosphate group for a substrate-binding site, thereby preventing the formation of an enzyme-phosphatidyl intermediate. This may be a conserved feature of PLD superfamily enzymes, (C) 1999 Federation of European Biochemical Societies.