506 



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



the presence of ethylenediaminetetra-acetate (EDTA) and by substrate 

 (lactate) (Morton, 1955a; Appleby and Morton, 1959b). Under some 

 conditions autoxidation leads to formation of HoOa, since catalase partially, 

 but not completely, protects against inactivation (Table 2). The formation of 

 H2O2 under these conditions may indicate a slow reaction of oxygen with the 

 flavin group (see Fig. 1), or, more hkely, autoxidation of some dissociated 

 flavin since free riboflavin phosphate may act as an acceptor with cytochrome 

 bo. Oxygen also reacts slowly with the haem group (Fig. 1 and vide infra). 

 Protection by EDTA is due to chelation of metals, such as copper, which 



Table 2. Protection of enzymic activity of crystalline cytochrome b^ 

 BY catalase 



Crystalline cytochrome b., (40 /(g/ml) in m sodium lactate at pH 68 was held aerobically with and 



without added crystalline catalase (about 100 /<g/ml). After storage, some of the material was further 



treated with hydrogen peroxide. Activities were determined at 18'C and at pH 80. The results are 



from Appleby and Morton (1959b). 



Table 3. Inhibition of enzymic activity of 



cytochrome b^ by Cu++ ions and protection 



by ethylenediamine tetra-acetate (EDTA) 



Crystalline cytochrome b.^ in 0-5 m sodium lactate at pH 6-8 was 

 held aerobically at 0° for 18 hr, with and without the additions 

 indicated. Activities are expressed as //moles of ferricyanide 

 reduced/hr/ml of enzyme at 18°C and at pH 80. The results are 

 from Appleby and Morton (1959b). 



With anaerobic storage, activity 179. 



