The electrometric titration of hemin and hematin

It was shown 5 years ago (1) that the change from methemoglobin to hemoglobin could be studied by an electrochemical method. The reduction by means of sodium hydrosulfite and the oxidation of the reduced compound (hemoglobin) by ferricyanide were found to involve 1 equivalent. These results have been confirmed and extended in later work (2). An application of the same method to a study of the reduction of alkaline hematin solutions (1) yielded uncertain results which seemed to indicate that 2 equivalents of hydrogen were involved in the reduction of this compound. No definite conclusion could be drawn from the data, however. A continuation of this work has now shown that satisfactory electrochemical titration curves may be obtained if titanous tartrate is employed as the reducing agent. The results are very definite and show that the change involves only 1 equivalent.