CAT{RON MONOXIDE IMII liTTOUS '.V2\ 



Chance speaks of are satisfied, how can we be sure that we don't have other effects 

 in a system like that? 



Krall: One should run an action spectrum. However the yellow lif:;ht from a 

 sodium lamp is practically monochromatic, and acts on this system the same as 

 white light for reversal under low oxygen pressures. This indicates that there is not 

 an odd cytochrome oxidase that would have a photodissociation spectrum different 

 from the cytoirhrome oxidase in animal systems. 



Amon : My point goes bej'ond that. My point really is, how can you ever inter- 

 pret the effect of an inhibitor, such as carbon monoxide or any other inhibitor, on 

 the whole leaf in terms of a .single process? 



Krall : The only way I can answer that is to quote W. O. James' article on re- 

 spiratory inhibitors in "Annual Reviews of Plant Physiology." He states that re- 

 versal of carbon monoxide inhibition by light of a specific wavelength is probably 

 the most elegant test we have in vivo of testing for an enzyme activity. 



Chance: Now you are talking again.st the man you are working for, Dan! 



Gaffron: First, photosynthesis and carbon monoxide in this sort of experiment 

 have a long history. One can read in Rabinowitch's book about some Italians who 

 claimed that photosynthesis is inhibited by carbon monoxide. Many people have 

 tried but could not repeat their experiments. On account of my own experiments 

 with carbon monoxide, I came to the conclusion that if one does anaerobic experi- 

 ments he has to be sure to exclude a round-about way of inhibition. If one puts 

 aerobic plants into nitrogen or carbon monoxide they don't like it, which is ex- 

 pressed by the fact that after a while the subsequent photosynthesis is seen to be 

 inhibited. Long anaerobic dark periods cause long induction periods for photo- 

 sj-nthesis. Quick, yet complete, removal of oxygen does not produce an inhibition. 

 Its cause is, therefore, not lack of oxygen as such but a consequence of anaerobiosis. 



If this inhibition is relieved by oxj-gen, then we may say it is a respiration which 

 does away with the inhibition. By using carbon monoxide instead of nitrogen or 

 helium one prevents this function of respiration. The inhibition persists and one 

 can shine as much red light on it as one wants. If, however, a wavelength is used 

 which is very effective for the release of the carbon monoxide inhiliition of respira- 

 tion, then photosynthesis has a chance to start again. 



This was one explanation I discussed at the time, but I added that sometimes I 

 saw an effect of carbon monoxide which cannot quite be explained away in this 

 round-about manner; for instance, its persistence in the presence of some oxygen. 

 A direct inhibition by CO of a "photocatalase," that is of an iron-porphyrin 

 enzyme in the oxygen-evolving systems was the alternative hypothesis. Now, 15 

 or 20 years later, we may have learned something. I have nothing against the 

 theory that cytochromes play a role in photosynthesis and that this role may con- 

 sist in creating energy-rich phosphate bonds by back reactions. 



The question now is, do you believe in a direct carbon monoxide inliibition of 

 photosynthesis? I think we don't have enough experiments. 



Whittingham: Dr. Krall, have .you any data on the time cour.se of the pho.s])ho- 

 rylation with or without CO? 



Krall : Very little. 



Whittingham : In observations in the light, on phosphate fixation, did you attain 



