The reaction between metmyoglobin and hydrogen peroxide

Abstract

Transient complexes with well defined spectro- scopic characteristics play an important role in the reaction of the haemoprotein enzymes, catalase and peroxidase, with hydrogen peroxide.Two and sometimes three different complexes can be ob- served depending on the experimental conditions.For example, Keilin & Mann (1937) obtainedtwo red complexes with peroxidase and hydrogen peroxide, and later Theorell (1941) showed that a green com- plex preceded the formation of the first red complex.This system has been studied intensively by Chance (1949 a, b) who extended the observation to systems of catalase and hydrogen peroxide or alkyl hydroperoxides (1949c).There is, however, very little information from which structural differences accounting for the various complexes can be inferred.The transient nature of the complexes leads to experimental difficulties.These difficulties were absent in the case of the complex formed with metmyoglobin (MetMb) and hydrogen peroxide.The existence of a well defined red complex in this system and with haemoglobin too is well established.Keilin & Hartree (1935) found that the formation requires 1 molecule of hydrogen peroxide per haematin iron atom.With reducing agents the complex is reduced back to metmyoglobin or methaemoglobin.As far as is known, only this single complex is formed and because it shares certain properties with the secondary complexes of peroxidase and catalase, a detailed knowledge of its behaviour is valuable for the further elucidation of enzyme reaction mech- anisms.