Analysis and Interpretation of Absorption Spectra of Haemin Chromoproteins 151 



(1) The determination of haemin iron is most unequivocally and quantita- 

 tively accomplished through the characteristic absorption in the visible region 

 of the cyanide derivatives of haemin and the haemin proteins (Drabkin, 

 1942a, 1949b), and the spectra are remarkably similar in both the visible and 

 ultra-violet regions (Figs. 2 and 6). These findings indicate that a single major 

 molecular characteristic is responsible for the general over-all spectrum. In 

 the writer's analysis for iron by the 1 : 10-phenanthroline method the e value 

 for the maximum of ferrous 1 : 10-phenanthroline was found to be close to 

 identical with that of the cyanide derivatives of the haemin complexes 

 (Table 1 and Fig. 2). Accordingly it was deduced that in the analytical 

 procedure iron was liberated from one complex (hexaco-ordinated haemin 

 iron; Drabkin, 1936, 1938) and bound up in another, diimine iron (Drabkin, 

 1941b). The similarity of the spectra favoured the idea of a spectroscopically 

 operative structural similarity in these different classes of compounds. The 

 spectroscopic similarity of the cyanide derivatives of the ferrichromoproteins 

 has its counterpart in their low paramagnetic susceptibilities (Coryell, Stitt 

 and Pauling, 1937; Theorell, 1941). It was deduced from their magnetic 

 behaviour that they are essentially (though not fully) octahaedral d'^sp^ co- 

 valent bonded stabilized structures, in essence of the Werner hexaco-ordina- 

 tion type (cf. Pauling, 1940, 1948, 1949). 



(2) In Table 2 it may be seen that in some haemin complexes only a limited 

 number of the bands, postulated by the analysis, are represented by definite 

 maxima in the absorption spectra. However, considering the data on the 

 different haemin complexes as an interrelated whole, maxima representative 

 of at least eight, possibly nine bands (numbers « = 3 to 1 1) of an equally 

 spaced frequency distributed series are found. As has been stated, the 

 spectrum of ferrocytochrome c (Drabkin, 1941a) proved to be particularly 

 rich in maxima (Fig. 7) and disclosed the presence of bands missing from the 

 earlier examined spectra of haemoglobin derivatives, but 'predicted' by the 

 analysis. The basis for these differences in the spectra of reduced and 

 oxidized cytochrome c and haemoglobin derivatives is not clear, unless it 

 can be attributed to the difference in the bonding of the haemins with the 

 protein (Theorell, 1938, 1941). With the exception of small 'shifts' in the 

 location of some of the maxima, such spectral differences are erased in the 

 spectra of the respective cyanide derivatives of these chromoproteins (Fig. 6). 



(3) An examination of Table 2 will disclose that bands number 3, 6, 9 

 and 11 in the series Vq x 10^^ = 40 can also be distributed at regular fre- 

 quency intervals on the basis of Vq x 10"^ = 60. In the latter case the /9 

 band would be included as number 3 and the bands would be represented by 

 n = 2, 3, 4, 5, 6 and 7, with number 5 in an intermediate position between 

 7 and 8 of the spacing Vq x 10"^ = 40. The 60 spacing was originally assumed 

 (Drabkin, 1934), and led to the analysis, illustrated for the spectrum of 

 cyanmethaemoglobin, in Fig. 8. In this figure it may be seen that, utilizing 



