Reactions between haemin and hydrogen peroxide. Part 2.—Destructive oxidation of haemin

Abstract

The protoporphyrin ring of haemin (A) undergoes oxidative cleavage by hydrogen peroxide, yielding biliverdin (A). This reaction accompanies and complicates kinetic studies of the catalytic decomposition of hydrogen peroxide by haemin (A). This paper reports spectrophotometric studies of the kinetics of the oxidation of haemin (A), to beliverdin (A), at 0°C, in the pH range 6.82–8.43, using the method of initial rates. The reaction is first order with respect both to haemin (A) and hydrogen peroxide. pH effects indicate that haematin (A) is oxidized much more readily than haemin (A) itself. Changes in optical density, which occur rapidly after mixing reaction solutions, are consistent with the formation of a haemin (A)+ hydrogen peroxide complex.