Amine oxidase: XI. Beef plasma amine oxidase, a sulfhydryl protein

Abstract

The beef plasma amine oxidase has been shown to be a sulfhydryl protein containing about 2 —SH groups per mole of enzyme. The —SH groups are buried at pH 7.0 but become accessible to p-chloromercuribenzoate at pH 4.6 or at pH 7.0 in the presence of 8 m urea or 5 m guanidine hydrochloride solutions. The —SH groups are not essential for activity nor are they chelated to the copper present in the enzyme. At higher concentrations, p-chloromercuribenzoate inhibits the enzyme, noncompetitively. Since benzoic acid and benzyl alcohol also inhibit the enzyme, noncompetitively, it is postulated that there may be η-bonding between the inhibitors and an aromatic residue in the enzyme. The enzyme was found to be rapidly inactivated in 8 m urea and 5 m guanidine hydrochloride solutions.