The action of nitrite on haemoglobin in the absence of oxygen

Abstract

Much work has been done on the action of nitrite on haemoglobin, but there is little agreement on the course of the reaction. In the presence of a reducing agent Haldane (1901; Haldane and others 1897) detected only the formation of NO-haemoglobin (the compound formed by the action of nitric oxide on reduced haemoglobin) ; in the presence of oxygen a mixture of methaemoglobin and NO-haemoglobin was apparently obtained (cf. Haurowitz 1924 ; Meier 1925). On the other hand, Hartridge (1920-1) believed that in the presence of oxygen one compound, nitrite-methaemoglobin, was formed. The constitution of NO-haemoglobin, usually assumed to be a ferro-compound of the same type as oxyhaemoglobin or CO-haemoglobin, is also doubtful. Anson and Mirsky (1925) state that NO-haemoglobin is a ferri-compound, the first product of the reaction between NO and haemoglobin being methaemoglobin which then combines with NO. The presence of oxygen probably complicates the reaction between nitrite and haemoglobin. If the mechanism involves HNO 2 the presence of oxygen may result in an ill-defined concentration of NO. In addition, although the oxidation of haemoglobin to methaemoglobin by oxygen is relatively slow (Brooks 1931, 1935) nitrite may act as catalyst. Finally, in the presence of oxygen and excess nitrite compounds other than methaemo-globin and NO-haemoglobin are certainly formed (Meier). For these reasons the reaction was studied quantitatively in the absence of oxygen.