Phospholipase C fromBacillus cereushas sphingomyelinase activity

Purified, electrophoretically homogeneous phospholipase C (PLC) preparations can be separated into two peaks by isoelectric focusing in sucrose gradients. The main peak has an isoelectric pH of 6.6-6.8 and contains two Zn2+ per molecule. The more acid peak (isoelectric pH about 6.2) contains about one Zn2+ per molecule and has a markedly reduced specific activity which can be raised by adding Zn2+. The purified enzyme has a low sphingomyelinase activity which coincides completely with the lecithinase activity in fractions from isoelectric focusing. The sphingomyelinase activity was greatly enhanced by substitution of Co2+ for Zn2+ but remained essentially unaltered when the levels of Ca2+ and Mg2+ were changed. These findings provide evidence that the sphingomyelinase activity is a true endogenous activity of PLC and not caused by contaminating sphingomyelinase.