HE.MICHROMES 177 



In Table IV the most reliable quantitative data on the extinction 

 coefficients of some hemochromes are collected, together with the 



TABLE IV 

 Spectrophotometric Data of Hemochromes in the Visible Region 



"On treatment with hij-droxylamine the band is shifted 25 m/z toward violet to the 

 position of protohemochrome, the oxime ( — CH = XOH) group having a similar 

 spectral influence to the vinyl group ( — CH = CH2). 



''The lower values refer to a solution in 0.2 A' XaOH, the higher ones to a solution 

 of pH 4.5. 



band positions of a number of others. The influence of variation of 

 base and porphyrin can be clearly seen. 



4.2. Hemichromes 



All hemochromes react with atmospheric oxygen, their bivalent 

 iron being oxidized to the trivalent state with the formation of hemi- 

 chromes. The velocity of autoxidation is closely connected with the 

 oxidation-reduction potential of the particular hemochrome/hemi- 

 chrome system {179, cf. Section 7.). 



4.2.1. Stability of Hemichromes. Keilin (1475) held that hemi- 

 chromes (parahematins) are stable only at a pH near the neutral 

 point, and dissociate into hematin and nitrogenous compound in 

 more acid or more alkaline solutions. While this is possibly correct 

 for denatured globin hemichrome {cf., however. Chapter VI, 2. 4. '2), 

 it certainly does not hold in general. Thus, from the study of absorp- 

 tion spectra {1S0;1687, p. 242) as well as from Barron's and Clark's 

 studies of the oxidation-reduction potentials {cf. below), there is 



