02 UPTAKE IN R. VANNIELII 

 TABLE 3. 



329 



Effect of light and oxygen on cytochrome oxidation 

 in intact cells of R. vannielii (4) 



Anaerobic, 



light minus 



dark 



Aerobic, 



light minus 



dark 



Dark, 



aerobic minus 



anaerobic 



AO.D. 



(422.5-440 m^) 



-0.0027 



-0.0019 



-0.0018 



540 



W L 



560 

 (mp) 



red/ox. 

 anaer/aer. 

 in light 



anaer/aer 

 dark 



580 



Fig. 1. Difference spectrum, anaerobic vs. aerobic, 

 of intact cells of R. vannielii in the light and dark. 



Dark Oxidase. 



Carbon monoxide and cyanide inhibited oxygen uptake in the dark. 

 A mixture of carbon monoxide and oxygen (9:1, v/v) caused a 55 per 

 cent inhibition. The concentration of cyanide required for 50 per cent 

 inhibition was lO"^-'^ M. 



The inhibitory effect of carbon monoxide and the presence of a 

 CO-binding hemeprotein in this organism (3) suggests that this heme- 

 protein is acting as the terminal oxidase in dark respiration. It is of 

 significance that the CO-binding hemeprotein is localized primarily in 

 the components of the cell containing the least pigment. 



The difference spectra shown in Fig, 1 indicate that cytochromes 

 c-553 and 6-563 are involved in oxygen uptake in the dark. 



