about 16 to about 22 carbon atoms, and R is a polar group selected from the group consisting of oxy radicals of choline, ethanolamine, inositol, serine, glycerol, and alkanols having from 1 to 4 carbons; b) incubating a cytosolic phospholipase A2 enzyme with said solution; c) adding an enzyme quenching reagent to said solution; d) adding a thiol-sensitive reagent to said solution; and e) measuri