Studies on the oxidation-reduction potentials of hemoglobin were initiated by Conant (1) with Fieser (2), Scott (3), and Pappenheimer (4), who showed that the system was thermodynamically reversible, and explored the relation of E&l to pH. Since the hemoglobin system is electromotively sluggish, a great advance was made with the introduction by Taylor and Hastings (5) of electromotively active mediators which permit the rapid attainment of a true equilibrium at the platinum electrode. With the aid of these mediators, a careful study of the oxidationreduction equilibrium of horse hemoglobin was achieved by Taylor and Hastings in 1939, and of ox hemoglobin by Havemann (6) in 1943.

As part of this work, the relation of Et to pH was extensively studied by the two authors (5, 6). There is a substantial agreement between the results in spite of the species difference and of the slight differences in methods used. In both cases, the Eg pH curve, which is the analogue of the oxygen Bohr effect (7), passes from essentially zero slope at low pH to a slope of 0.06 at high pH, the latter value indicating a difference of one proton between ferrohemoglobin and ferrihemoglobin at alkaline pH. Havemann also studied the effect of temperature, and reported a set of Et pH curves at different temperatures from 10-45”. A particularly interesting problem is raised by the observation of Taylor and Hastings that the oxidation-reduction equilibrium curve is asymmetrical, the value of n (at pH 7) changing progressively from 1 to 2 as the oxidation proceeds. Here n is defined by