Phospholipase C from Bacillus cereus has sphingomyelinase activity

Abstract

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.

Key-words:

• Isoelectric focusing
• metal ions
• phospholipase C
• sphingomyelinase