Analysis and Interpretation of Absorption Spectra of Haemin Chromoproteins 145 



Concentration of Reference. The spectrum curves are plotted for a conven- 

 tional depth of 1 cm. The concentration of reference, unless otherwise indi- 

 cated, is 1 mM/L, where 1 niM represents 1 milliatom of iron. The iron content 

 was determined independently (Drabkin, 1941b), but the spectrophotometric 

 determination of the extinction at the maximum in the region of 545 to 



170 180 190 200 210 220 



K 



510 



Fig. 2. Absorption spectrum curves of complexes of iron. Curve 1 , ferrous 1 : 10- 

 phenanthroline (ferrous o-phenanthroline). Curve la, ferrous dipyridyl complex. 

 Curve 2, cyanmethaemoglobin (ferrihaemoglobin monocyanide). Curve 2a, 

 haemin dicyanide (ferriprotoporphyrin dicyanide). The e (c = 1 mM/1.) for 

 ferrous 1 : 1 O-phenanthroline is 11 -05 at the maximum of 500 m//, read against an 

 appropriate blank. The open circle corresponds with a value of 11-25 for this 

 complex read against water. For details see Drabkin (1941b). (Absorption 

 spectra closely similar with those of cyanmethaemoglobin and haemin dicyanide 

 are yielded by the cyanide derivatives of the ferrihaemochromes, such as 

 monocyanide monopyridine ferriprotoporphyrin, with e = 11-7 for the maximum 

 at 545 m/t (Drabkin, 1942a) and by mesohaemin dicyanide and coprohaemin 

 dicyanide with maxima respectively at 537 and 535 m/<, displaced about 10m/< 

 toward the shorter wavelengths in comparison with protohaemin derivatives 



(Drabkin, 1942b).) 



535 m/f of corresponding cyanide derivatives of the ferri-complexes served 

 in the direct, unequivocal evaluation of haemin iron (Drabkin, 1942a and b, 

 1949, 1954). Table 1 and Fig. 2 supply pertinent information. It may be 

 noted that the writer's value of 0-338% for iron in haemoglobin (Drabkin, 

 1949b) has been tentatively accepted by the Protein Commission of the 

 International Union of Pure and Applied Chemistry (cf. Drabkin, 1957). 

 This iron content appears to be valid on a dry weight basis, and corresponds 

 with a 1-Fe-atom equivalent weight of 16,500 for haemoglobin and 15,850 

 for globin, the total molecular weight of which may be taken as 15,850 X 4 

 = 63,400. 



