Inactivation of Phospholipase C from Bacillus cereus by a Carboxyl Group Modifying Reagent.

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Abstract
Phospholipase C [EC 3.1.4.3] from B. cereus was inactivated by incubation with either of the carboxyl reagents, a water-soluble carbodiimide plus a nucleophile or Woodward''s reagent K. With the former reagent, the incorporation of the 1st mol of nucleophile caused a 4- to 5-fold increase in the Km for dihexanoyllecithin with no significant effect on the Vmax. The 2nd mol of nucleophile incorporated caused no further change in Km but destroyed most of the catalytic activity. Modification of the enzyme by carbodiimide plus nucleophile did not alter the relative activity of the enzyme towards micelles and monomolecularly dispersed solutions of diheptanoyllecithin. Inactivation by this reagent did not significantly decrease the ability of the enzyme to bind to a substrate-based affinity gel. Phospholipase C apparently contains a single carboxyl group that is essential for catalytic activity. The enzyme also contains a total of 4-5 reactive/exposed carboxyl groups.

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