Analysis and Interpretation of Absorption Spectra of Haemln Chromoproteins 167 



which measured the release of the enzyme from its carbonyl derivative 

 (poisoned state) had several maxima in the ultra-violet, including the y band. 

 This would not have been the case unless the bands had a similar molecular 

 origin. 



The a and (i bands, as disclosed by the analysis, do not belong to the main 

 spectral series, and have been shown to reflect more intimately the effect of 

 different co-ordinating ligands. A broad correlation has been found between 

 the paramagnetic susceptibilities and the corresponding spectral patterns in 

 the area covered by bands 4, a, (i and 5 (Table 3). This correlation would 

 appear to justify the deduction that the visible spectra reflect electron 

 transitions involved in the hybridization of the atomic s, p and d orbitals of 

 the iron cation (Pauling, 1949 ; Williams, 1956). Four major spectral patterns 

 have been uncovered, namely those of ferrihaem and its derivatives with 

 cyanide, and those of ferrohaem complexes with cyanide, pyridine or 

 globin, and carbon monoxide. Identical patterns (see the text and Figs. 

 15 to 17) are obtained for corresponding derivatives of proto-, meso- and 

 coprohaemin, except for the displacement of the maxima of the protohaemin 

 complexes toward the longer wavelengths. This displacement is also apparent 

 in the spectra of proto- and mesoporphyrin, and is regarded as the main 

 evident contribution of porphyrin />e/-5e to the over-all haemin protein spectra. 



Since the disclosure of the close similarity of the spectra of ferrous 1 : 10- 

 phenanthroline and the cyanide complexes of ferrihaemin derivatives 

 (Drabkin, 1941b, and Fig. 2), the structure of the ferrous diimine has been 

 shown to be Fe^Pheug (Gould and Vosburgh, 1942; Harvey and Manning, 

 1952) and the anomalous colours of the metallic diimines have been explained 

 as due to the resonance of 77-electrons (and their increased mobility in the 

 metal complex) over the non-metallic atoms composing the entire chelate 

 ring, assuming that ^/-electrons of the metal are involved in the formation 

 of the co-ordinate bond (Sone, 1952; Krumholz, 1953; see also Pauling, 

 1940; Calvinand Wilson, 1945; Chatt, 1949). Williams (1956) has used the 

 metallic diimines and the postulated electronic basis for their spectra as 

 models in his interpretation of the visible absorption spectra of the haemin 

 chromoproteins. 



The contribution of the protein moieties to the over-all spectra of the 

 haemin chromoproteins is not identifiable in any alteration in spectral 

 pattern, nor does it appear to be confined to a particular spectral region such 

 as 280-275 m^w. The role of the protein is postulated to be that of a 'resonator' 

 or 'enhancer'. The relative intensity of the bands, not their pattern, may be 

 influenced, analogously with the effect of the alkaline earth metals on the 

 emission spectrum of copper. 



The Graphic-mathematical Analysis. It must be frankly stated that this is 

 an empirical approach, and it is recognized that the solutions yielded by the 

 adopted analytical procedure are influenced by underlying assumptions. 



