Alkylation of horseradish peroxidase with lodoacetate

Abstract

A kinetic and chemical study of the inactivation of horseradish peroxidase by reaction with iodoacetate has been undertaken to gain insight into the chemical behavior and reactivity of the protein moiety with a view toward fully defining the catalytic site of the enzyme. It was concluded from a study of the effect of pH upon the rate of inactivation of the enzyme and from amino acid analyses of partially inactivated enzyme samples that the alkylation of methionine residues at acid pH values and the alkylation of histidine (and possibly lysine) residues at higher than neutral pH values were primarily responsible for horseradish peroxidase inactivation. Examination of the optical rotatory dispersion spectra (210–350 mμ) of partially inactivated horseradish peroxidase samples suggests that the tertiary structure of the enzyme is affected by the alkylation of methionine residues.