Analysis and Interpretation of Absorption Spectra of Haemin Chromoproteins 161 



spectra and the corresponding ones for MHb ^ MHbOH. The colours of 

 the spectroscopic species are reversed with reference to pH. MHb is brown, 

 MHbOH red, whereas in the pyridine complexes the colour is olive brown at 



D I 





-r 



Fig. 13. Absorption spectrum curves of solutions of crystalline human met- or 

 ferrihaemoglobin, buffered to various pH values. The solutions correspond to 

 those shown in Fig. 12, but the concentration of haemoglobin is 0-01 17 mM/1. Tsee 

 legend to Fig. 12). The e (lmM/1) values for the maximum of methaemoglobin 

 (pH 6-2) at 407 m/< and for the maximum of methaemoglobin hydroxide (pH 9-35) 

 at 415 m/i are 169 and 113 respectively. 



pH 11-38, red at pH 7-26. Uncertainties still exist as to the structure of 

 pyridine ferriprotoporphyrin (Davies, 1940) and magnetometric measure- 

 ments are available only for the hydroxy form (Rawlinson, 1940), which was 

 deduced to be essentially covalent in contrast with MHbOH (see Table 3). 

 Further information is required for the clarification of this situation, but at 

 present the spectra cannot be easily reconciled with the proposed correlation. 



