Analysis and Interpretation of Absorption Spectra of Haemin Chromoproteins 143 



series, had been demonstrated only in relatively simple molecules, such as 

 KMn04 (Hagenbach and Percy, 1922) and CoCU in concentrated HCl 

 (Erode, 1928). It was deduced that the absorption spectra of haemoglobin 

 derivatives were largely an expression of iron in a co-ordination complex, 

 and attention was called to certain similarities in the spectra of K3Fe(CN)g 



tOOO 900 800 700 600 500 400 300 200 



A, tn/^ 

 Infrared 4" Visible 4*— Ultraviolet " 



d ore =10-50 



d ore =1 



d ore =01 



Fig. 1. Absorption spectrum curves of oxyhaemoglobin, HbOj, deoxygenated 

 haemoglobin, Hb, and carbonyl haemoglobin, HbCO (Drabkin, 1950; Gordy 

 and Drabkin, 1957). The values of cuvette depth, d, or concentration, c, suggest 

 the relative thicknesses of layer or concentrations required for optimal spectro- 

 photometry in the different spectral regions, due to a 500-fold difference in the 

 densities of the maxima over the spectral range of 1100 to 200 m/<. The use of 

 log £ (the log of the molar or 1-Fe-atom equivalent extinction) permits the 

 portrayal of the maxima in region 1 together with the rest of the spectrum. Many 

 derivatives of the chromoproteins have weak bands in this region (the red and 

 near infra-red). As examples, proto- and mesohaemin hydroxides have maxima 

 in the region 810-820 m/<. Met- or ferrihaemoglobin hydroxide (alkaline methae- 

 moglobin, pH 9), the spectrum of which in the near infra-red was originally studied 

 by Horecker (1943), also has an absorption maximum at 820 m/< {v x 10~^ = 122), 

 with £ (1 mM/1.) = 0-544 and log E = 2-735 (Gordy and Drabkin, 1957). 



and cyanmethaemoglobin (Drabkin, 1936). The same deduction was later 

 made from the similar paramagnetic susceptibilities of these iron complexes 

 by Coryell, Stitt and Pauling (1937). The absorption spectrum curves were 

 resolved into component bands by means of a novel graphic-mathematical 

 analysis (Drabkin, 1937, 1938, 1940, 1950). Interestingly enough, the analysis 

 indicated that the a and ^ bands did not belong to the main spectral series 

 and that the band at 275 m^< was not primarily owing to globin (Drabkin, 

 1937, 1938). Furthermore, the analysis predicted the potential occurrence of 

 bands in the neighbourhood of wavelengths 833, 313 and 250 m/<. This was 



