The formation and properties of sulphmyoglobin and sulphcatalase

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Abstract
Sulphmyoglobin is formed stoicheio-metrically by the reaction of hydrogen sulphide and metmyoglobin peroxide. It combines with carbon monoxide, but not with oxygen, and is oxidized to metsulphmyoglobin by ferricyanide. Metsulphmyoglobin behaves like metmyoglobin. Its iron atom is co-ordinated with a water molecule dissociating under alkaline conditions; it forms fluoride, cyanide and azide complexes, and a metsulphmyoglobin peroxide compound. Myoglobin is re-formed from sulphmyoglobin by the action of azide or hydrogen peroxide; metsulphmyoglobin is slowly converted into metmyoglobin in the presence of cyanide. Ferrosulphcatalase is formed by the action of hydrogen sulphide on catalase compound II. It combines with carbon monoxide and is oxidized to (ferric) sulphcatalase by oxygen but not by ferricyanide. Sulphcatalase forms'' complexes with fluoride, cyanide, sulphide and azide; it is not reducible by dithionite, does not give an alkaline form and does not produce peroxide compounds. In the sulphide-sulphcatalase complex, the sulphide is inhibiting the same haem group in two ways; by irreversibly modifying the porphyrin and by forming a reversible complex with the iron. Catalase is regenerated from sulphcatalase by oxidizing agents such as oxygen and alkyl peroxides; its aerobic formation from ferrosulphcatalase is accelerated by cyanide, azide and fluoride. Sulph-compounds cannot be produced from any peroxidase peroxide compounds, nor from catalase compounds I or III. Hydrogen selenide does not have an analogous effect to that of sulphide. The results are discussed with reference to the problems of the chemical nature of both sulph-compounds and peroxide compounds and the possibility of the natural occurrence of slph-com-pounds.