Studies of the use of dihexanoyllecithin and other lecithins as substrates for phospholipase A: With addendum on aspects of micelle properties of dihexanoyllecithin

Abstract

Some properties of the phospholipase A from venom of Crotalus durissus terrificus have been studied using as substrate a water-soluble lecithin, dihexanoyl- l-α-glycerylphosphorylcholine (DHL). Ca ++ is required for activity, and the concentration required for maximal activation is about 0.004 M at pH 6.8–9.8. The pH optimum for the system in the presence of excess Ca ++ is pH 8. Ba ++, Zn ++, and Cd ++ inhibited the reaction. Inhibition by Ba ++ was competitive with Ca ++, and most probably involves a site on the enzyme. Caproate, one of the products of the enzymic reaction, has essentially no effect on the reaction even at levels 10 times that of the substrate. Hexanoyllysolecithin, the other product, had no effect when tested at 5 × 10 −5 M. The influence of other lysolecithins, sodium dodecyl sulfate, Tween 20, and Tween 80 on the activity of the enzyme toward DHL, and toward the water-insoluble dioctanoyl-, dimyristoyl-, and ovolecithin is also described. Studies on the micellar properties of DHL, with estimates of the critical micelle concentration and micellar weight are also presented.