The oxidation of haemoglobin to methaemoglobin by oxygen - II—The relation between the rate of oxidation and the partial pressure of oxygen

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Abstract
Neill and Hastings (1925) found that the rate of oxidation of haemoglobin by dissolved oxygen in aqueous solution was maximal at a small partial pressure of oxygen; a similar result was obtained (Brooks, 1929) for the oxidation of haemoglobin in pigmented muscle. In both cases the rate was determined approximately. A possible explanation of the effect was suggested to Neill and Hastings by the work of Conant (1923, 1924-25, 1926, 1928) who had shown that methaemoglobin and reduced haemoglobin formed an oxidation-reduction system of the ferri-ferro type. If only reduced haemoglobin reacts with oxygen to give methaemoglobin, increasing the oxygen pressure decreases the concentration of the other reactant (by the formation of oxyhaemoglobin), and a maximum rate of oxidation might be obtained. The rate of oxidation of haemoglobin, using ox-blood diluted in a phosphate buffer, was measured at a single oxygen pressure (Brooks, 1931) and found to be unimolecular with respect to the concentration of haemoglobin. Similar measurements at 30° C andph5·69 have now been made at other oxygen pressures; the concentration of oxy-and reduced haemoglobin in the system has also been determined. Fortunately, the establishment of equilibrium between oxygen and haemoglobin is very rapid in comparison with the rate of oxidation (Hartridge and Roughton, 1923, 1925).

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