E. M. JOPE 



changes in environment, such as salt and hydrogen ion concentration, 

 or concentration of haemoglobin itself, and to observe the effects of 

 drying and of denaturation. 



Denaturation of methaemoglobin by alkali, heat or strong urea has 

 no effect upon the peak wavelength of the Soret band. The effect of 

 denaturation upon the spectral absorption of Hb0 2 may be divided 

 into three stages, the first in which the Soret band peak changes to 

 about 410 m [i (Figure 2), the solubility in the isoelectric region remain- 

 ing, however, fairly high and some measure of reversible c ombination 

 with oxygen being retained ; the second in which the Soret band 

 shifts to 406 mjA, that of methaemoglobin, but the visible bands 

 remain as in Hb0 2 , and the final stage which appears to yield denatured 

 methaemoglobin. The intermediate stage resembles in many ways the 

 usual recombined haem-globin product (see p. 218). The first stage 

 occurs on prolonged standing of Hb0 2 , especially in dilute solution, 

 or in strong salt concentrations, and at room temperature. These 

 are conditions in which electrovalent links and hydrogen bondings in 

 proteins are weakened. D. L. Drabkin and J. H. Austin 5 observed 

 what may be a related effect in the visible spectrum of Hb0 2 on 

 standing in dilute solution. 



too 



HbO ? First Intermedia! 

 Denatured Stage and 

 Recombined HbO, 



J90 



4/0 420 

 A fm/t) 



Figure 2. Spectral absorp- 

 tion in the Soret band region 

 of haemoglobins, showing 

 effect of denaturation. 



Changes in hydrogen ion concentration have little effect upon the 

 Soret bands of the haem proteins. The Hb0 2 Soret band remains 

 constant in wavelength but is reversibly depressed by about 5 per cent 



208 



