The histidine residues of phospholipase C from Bacillus cereus

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Abstract
The inactivation of phospholipase C from B. cereus at pH 6 by diethyl pyrocarbonate paralleled the N-ethoxyformylation of a single histidine residue in the enzyme. The inactivation arose from a decrease in the maximum velocity of the enzymic reaction with no effect on the Km value. The inactivation did not apparently alter the ability of the enzyme to bind to a substrate-based affinity gel. The native enzyme contained only 1 reactive histidine residue. Removal of the 2 Zn atoms from the enzyme increased the number of reactive histidine resiues to 5, but in the totally denatured enzyme nearly 8 such residues were available for reaction with diethyl pyrocarbonate. The enzyme thus appears to contain 1 histidine residue that is essential for catalytic activity and 4 that may be involved in co-ordinating the Zn atoms in the structure.