The oxidation of myoglobin to metmyoglobin by oxygen. 1

Abstract

The autoxidation of myoglobin to metmyoglobin in air at 30[degree] in 0.6 [image] phosphate buffer of pH 5.69 was studied at several different concns. and using 5 prepns. of recrystallized myoglobin. The reaction was shown to be 1st order with respect to unoxidized myoglobin and the mean value of the 1st order rate constant was 0.325 [image] 0.015 hr.-1. Both spectrophotometric and O2 absorption methods of analysis were used. The 1st order rate constants obtained by these methods were in agreement. Under the conditions of the expts. it was shown that no detectable denaturation of the protein or choleglobin formation occurred. Measurement of the O2 absorption of the reaction showed that 2.5 moles of O2 were used for each mole of metmyoglobin formed, strongly suggesting that H donor groups on the protein molecule are involved. Thus in contrast to the intramolecular mechanism of the reaction postulated by Lemberg and Legge (1949) the reaction must be intermolecular. In view of the similarity of the kinetics of the autoxidation of myoglobin and haemoglobin, doubt is cast on the idea of an intramolecular mechanism in the case of the autoxidation of hemoglobin.