Investigation of the mechanism of phosphonoacetaldehyde hydrolase

The authors are presently studying enzymes which catalyze the formation and cleavage of carbon phosphorous bonds. In 1970 LaNauze et. al. reported the isolation of one enzyme of interest - phosphonoacetaldehyde hydrolase from a mutant of Bacillus cereus. This enzyme catalyzes the hydrolysis of phosphonoaldehyde to acetaldehyde and inorganic phosphate. They have isolated phosphonatase from wild type B. cereus (grown on 2-aminoethylphosphonate as the P/sub i/ source) and have used 1H-NMR and 31P-NMR techniques to determine the products of the enzyme reaction as phosphate and acetaldehyde. The mechanism of the enzyme could involve the formation of a Schiff base between phosphonoacetaldehyde and lysine or it might only require Mg++, an essential cofactor for activity. To distinguish between these possibilities they have begun to look at the Schiff base formation in more detail. NaBH4 was found to inactivate the enzyme in the presence of substrate but not in its absence. This is consistent with results obtained for the enzyme isolated from the mutant bacteria. In addition treatment of the wild type enzyme with tritiated NaBH4 resulted in significant incorporation of radiolabel into the protein as compared to the control. These results tentatively suggest that hydrolysis proceeds via a covalent imine intermediate