The Reduction of Methemoglobin by Ascorbic Acid* by Carl S. Vestling

In this laboratory a study of the oxygen capacities of chemically modified hemoglobins has recently been undertaken. In connection with this work the reduction of methemoglobin under carefully controlled conditions offered itself as a problem, since the combination of a ferriheme with globin leads to methemoglobin. In view of this consideration and of the recent reports of Cox and Wendel (l), Morrison and Williams (2), Gelinsky (3), and others on the reduction of methemoglobin in viva, and those by Lemberg and coworkers (4, 5) on the coupled oxidation of ascorbic acid and hemoglobin, it was decided to make a study of the reaction between methemoglobin and ascorbic acid in vitro. This reaction is of particular interest, since it forms one step in the cycle postulated by Lemberg, Legge, and Lockwood (6) for the formation of choleglobin (and bile-pigments). It has been found in accordance with thermodynamic prediction that ascorbic acid at pH 7 and 0” will reduce methemoglobin to the extent of 80 to 90 per cent within 6 hours. When the reaction is carried out at room temperature in the presence of methylene blue, interaction between the two systems is complete at the end of 1 hour. The accompanying reactions have been studied by the oxygen capacity method.