Spectrokinetic studies of the reaction of hydrogen peroxide with haemoglobin in dithionite solutions

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Abstract
The reaction between hemoglobin, dithionite and hydrogen peroxide was investigated by spectrokinetic measurements. The results show that by reaction with the peroxide, hemoglobin is largely converted into an unstable derivative, which persists for a definite period, and is then largely reduced to hemoglobin by the excess of dithionite. In the overall reaction, part of the hemoglobin is destroyed, and small amounts of choleglobin are formed at pH 7-10 and of sulphemo-globin at pH 6. The intermediate compound is probably methemoglobin-hydrogen peroxide, which exists in a mixture with a small proportion of a substance subsequently converted into choleglobin. A new unstable intermediate has been detected in the reaction at pH 8.5-9.5 in the presence of carbon monoxide, which is characterized by a maximum at 600 mu, and is slowly but quantitatively converted into caroxycho-leglobin in the presence of excess of dithionite. The addition of hydrosulfide to a reacting mixture of hemoglobin, dithionite and peroxide during the life of the peroxide intermediate at pH 8.5-9.5 at once gives a large yield of a derivative with the spectroscopic properties of sulphemoglobin. A mechanism is discussed for these reactions. Experiments indicate that myoglobin is temporarily but completely converted into metmyoglobin-hydrogen peroxide on treatment with hydrogen peroxide in the presence of excess of dithionite. Small amounts of pigment were destroyed in the overall reaction, but there was no evidence of the formation of cholemyoglobin or other green pigments. The explanation previously advanced for the action of oxygen on hemoglobin solutions containing dithionite was confirmed.