82 



K. Kaziro and K. Tsushima 



The sigmoid coefficient of the curves obtained with haemoglobin and EIC 

 at any pH tested was found to be constant. In contrast, the affinity of haemo- 

 globin to EIC was influenced by the change in pH. 



100 



E 50 



Free ethylisocyonide, 



IQ-^ 



molesA 



Fig. 2. EIC equilibrium curve of reduced haemoglobin. The measurements were 

 made at pH 6-8 and at 25°C. 



pH 

 Fig. 3. pH dependence of Kso. Concentration of urea: I, none; II, 6-0 M. 



The curve in Fig. 3 (I) is a theoretical curve which was obtained by intro- 

 ducing the values of pX^ and pA'a of haem-linked acid groups of oxyhaemo- 

 globin to Wyman's equation (Wyman, 1948). 



As seen from Fig. 3 (I), the experimental values coincide closely with the 

 theoretical curve. The results indicate that there exists a definite Bohr effect 



