508 



R. K. Morton, J. McD. Armstrong and C. A. Appleby 



Morton, 1959). The positions and extinction coefficients of the a, /i and y- 

 bands of reduced cytochrome bo (Fig. 2 and Table 4) are very close to those of 

 pyridine protohaemochrome and suggest that positions 5 and 6 of the iron 

 atom are co-ordinated with strongly basic groups. Since Ehrenberg and 

 Theorell (1955) found that the a-NHa group of glycylglycine and the e-NHg 



*fr.V 



300 400 



Wavelength, 



m/f 



Fig. 2. Absorption spectra of cytochrome b.^. Crystalline cytochrome b.. (de- 

 oxyribonucleoprotein) at pH 6-8: 

 (A) reduced with lactate; 

 (J5) oxidized; 



(C) oxidized riboflavin phosphate at a concentration equivalent to that of 

 the flavin in cytochrome bo. 



group of lysine do not readily co-ordinate with the iron of either ferri- or 

 ferro-protoporphyrin, it seems probable that at least one of the groups 

 involved in co-ordination is an imidazole nitrogen of a histidine residue. 

 There are 6 such residues/mole of haem (Table 1). 



The absorption spectra of lactate-reduced cytochrome ^2 ^t pH 4-7, 6-5 

 and 100 are shown in Fig. 3. At pH 10-0, the solution was strongly fluor- 

 escent, indicating extensive dissociation of the riboflavin phosphate, but there 

 was no detectable shift in the positions of the a-, /i- or y-bands of the haemo- 

 chrome. However, as compared with the spectrum at pH 6-5, the spectrum 

 at pH 4-7 and 100 shows a decrease in the ratio of fj.^banci/^a-band- The 

 increased absorption in the region 440-500 m/i at pH 10-0 as compared with 



