n-acetylmethionine and potassium-bromide

Urate oxidase from Candida utilis, an enzyme containing an essential thiol, was examined for its sensitivity to lactoperoxidase, an oxidant present in breast milk. Upon exposure to a system composed of lactoperoxidase, hydrogen peroxide and bromide at moderately alkaline pH, the urate oxidase exhibited comparable activity to the untreated enzyme; but upon exposure at moderately acidic pH, it lost its activity completely. Thus the lactoperoxidase-H2O2-bromide system significantly inactivated urate oxidase only at moderately acidic pH. This inactivation was prevented by the presence of N-acetylmethionine, a methionine analogue, or glutathione, which is a thiol compound analogous to an amino acid, indicating that it was probably due to the oxidation and damage of the methionine residue and/or the thiol group in the urate oxidase by the lactoperoxidase system, that loss of catalytic activity of the urate oxidase occurred.

Topics: Bromides; Candida; Glutathione; Hydrogen Peroxide; Hydrogen-Ion Concentration; Lactoperoxidase; Methionine; Potassium Compounds; Urate Oxidase