160 



David L. Drabkin 



D I 



Fig. 12. Absorption spectrum curves of solutions of crystalline human met- or 

 ferrihaemoglobin, buffered to various pH values. All the buffers had an ionic 

 strength, /<, of 0-1. D is the optical density. The spectra were obtained with the 

 General Electric recording spectrophotometer on solutions with a haemoglobin 

 iron concentration of 0-0584 mw/l. (Figs. 12 and 13 are supplementary.) Curve 

 1, methaemoglobin at pH 6-20 (taken as species 1). Curve 2, methaemoglobin 

 hydroxide at pH 9-35 (taken as species 2). The nine intermediate curves represent 

 mixtures of the two species at respective pH of 6-61, 7-05, 7-34, 7-7, 8-17, 8-50, 

 8-60, 8-80 and 9-20. Methaemoglobin hydroxide has an additional maximum at 

 820 m/< and there is an additional isosbestic point for the two species at 845 m/t 

 (Gordy and Drabkin, 1957). For the earlier work on the equilibrium of methae- 

 moglobin-methaemoglobin hydroxide and the treatment of spectrophotometric 

 data in a two component system see Austin and Drabkin, 1935. 



