Effect of Some Divalent Metal Cations on Phospholipase C from Bacillus cereus.

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Abstract
Incubation of phospholipase C from B. cereus with certain divalent metal cations caused enzyme inactivation, with Cu(II) being particularly effective. The inactivation arose from the reversible exchange of Zn(II) in the enzyme with the metal cations. Both Zn atoms in the enzyme exchanged rapidly with Cu(II); only one exchanged spontaneously with Co(II). With lecithin substrates, CoZn-phospholipase C had a specific activity of 3.6-11.3% of that of ZnZn-phospholipase C, whereas the CoCo-enzyme was < 1% active relative to the native enzyme. The CoZn-enzyme had the same Km value for dihexanoyllecithin as had the native enzyme, but the Vmax value was markedly lower. ZnZn-, CoZn- and CoCo-phospholipase C had very low activities towards sphingomyelin micelles, although for the CoCo-enzyme, the sphingomyelinase activity was 4- to 7-fold greater than for the native enzyme.