320 A. -R. KRATJ. 



mixture containing 5% oxygen gives a rate of P^- esterification ap- 

 oroaching that found under normal photosynthetic conditions in air 

 and white Hght. Participation of a cytochrome oxidase in the esterifi- 

 cation reaction is postulated. 



Acknowledgment. The advice and assistance of Doctors A. II. Brown and 

 E. Tolbert concerning preparation of this manuscript is gratefully acknowl- 

 edged. 



Discussion 



Whittingham : How long was the system illuminated? 



Krall: I worked with whole barley leaves and illuminated the plant in air with 

 2,000 footcandles of white light from a 150-watt reflector flood lamp for two hours. 

 This is a control experiment with four other experiments which you will see on 

 subsequent slides. 



Vernon : I would like to ask Dr. Smith if she has any evidence that this yellow 

 pigment, or the carbon monoxide binding pigment, might be active in the other 

 terminal oxygen system involved in the oxidation of succinate in the chromato- 

 phores. In other words, do these oxidize the carbon monoxide binding pigment? 



Lucile Smith : No, I don't have any evidence on that. The thing that is definite 

 is that the yellow pigment as now isolated is not capable of oxidizing reduced 

 R. riihrum cytochrome cj. It is not the cytochrome Ca oxidase. 



Chance : '\r^Tlat was the effect of oxygen tension on the degree of CO inhibition? 



Krall: There was no reversal in the absence of oxygen and practically no re- 

 versal with only 1 per cent oxygen. Five per cent oxygen achieved what might be 

 called about a 40 per cent reversal, at least not complete reversal. 



Chance: Are there enough data to demonstrate what one would call Oj-CO 

 competition? 



Krall : The evidence indicates that it may exist. 



Chance : Did you get a partition coefficient? 



Krall : No. 



Chance : If you could get an oxygen carbon monoxide partition coefficient for 

 this inhibition, then you would really tie it down as involving oxygen. The way it is 

 now it seems to me that the inhibiting effect of the CO could or could not involve 

 oxygen. 



Krall: I have studied the effect of CO on C^^Oa uptake. 19:1 and 9:1 ratios 

 showed the right competition coefficient. There was about a 50 per cent inhibition 

 at 9 : 1 and about 95 per cent inhibition at 19 : 1. 



Chance : The second point is that the verj^ high CO/Oj ratios would give j'ou 

 very little photo-dissociation of the carbon monoxide compound. 



Krall : That is why there is little reversal at 1 per cent oxygen. At ratios as high 

 as 400 : 1 carbon monoxide to oxygen, there was no reversal at all. 



Amon : You interpret all the effects of carbon monoxide as having been limited 

 to cytochrome oxidase. Is this justified in this complex system? Granted that we 

 know what carbon monoxide will do and assuming that those conditions that Dr. 



