MAMMALIAN PHOSPHOLIPASE-D - ACTIVATION BY AMMONIUM-SULFATE AND NUCLEOTIDES

Phospholipase D (PLD) associated with the rat kidney membrane was acti vated by guanine 5'-[gamma-thio] triphosphate and a cytosol fraction t hat contained ADP-ribosylation factor, When assayed by measuring the p hosphatidyl transfer reaction to ethanol with exogenously added radioa ctive phosphatidylcholine as substrate, the PLD required a high concen tration (1.6 M) of ammonium sulfate to exhibit high enzymatic activity . Other salts examined were far less effective or practically inactive , and this dramatic action of ammonium sulfate is not simply due to su ch high ionic strength. Addition of ATP but not of nonhydrolyzable ATP analogue adenosine 5'-[beta,gamma-imido] diphosphate further enhanced the PLD activation approximate to 2- to 3-fold. This enhancement by A TP needed cytosol, implying a role of protein phosphorylation. A surve y of PLD activity in rat tissues revealed that, unlike in previous obs ervations reported thus far, PLD was most abundant in membrane fractio ns of kidney, spleen, and liver in this order, and the enzymatic activ ity in brain and lung was low.