Abstract
Activities of membrane-associated phospholipases A 1 and A 2, and membrane-associated as well as soluble lysophospholipases were measured in different subcellular fractions of rat liver, using suspensions of stereospecifically labelled radioactive phospholipids as substrates. Plasma membranes and endoplasmic reticulum were shown to contain phospholipase A 1 and lysophospholipase activities, both of which could be stimulated by Ca 2+, mitochondria Ca 2+-dependent phospholipase A 2 and cytosol Ca 2+-independent lysophospholipase activities. Each of these lipolytic enzymes could be inhibited by antimalarial drugs (chloroquine, mepacrine, primaquine) at concentrations above 1 · 10 −4 M. Inhibition of the alkaline cytosolic lysophospholipase by these drugs was noncompetitive with respect to the substrate, and the inhibitory potency increased, when the pH was raised.
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