PRIMARY HYDROGEN ACCEPTOR ISOLATION 331 



P^* ill this area has been shown to cochromatograpii partly with 

 uridylic, cytidylic, and adenylic acids, the first one being quantita- 

 tively most important. Some of the label is found in a separate frac- 

 tion when chromatographed bj^ a formate-Dowex 1 procedure de- 

 signed to separate the mononucleotides of nucleic acids. This un- 

 known, believed to be the part of 5b which is convertible to 5a, has no 

 260-m^ absorption, but does have absorption below 240 niju. 



The 5a area contains but one compound. This was ascertained by 

 paper chromatography, wherein all the isotopes incorporated into 

 the material — phosphorus, carbon, and sulfur — move to but one spot 

 on the paper. The Rf value of this spot is about 0.4 in the phenol- 

 water solvent and 0.1 in the butanol-propionic acid developer. 5a 

 gives a positive reaction with the iodine-azide reagent, indicating 

 presence of an — SH group or "masked" — SH. Disulfide bonds do not 

 react with this reagent. 5b does not react with the reagent although 

 it does contain sulfur, which moves to the same spot on paper as does 

 5a. So far, no positi\'e test has been obtained for thioctic acid by the 

 manometric assay of (2) but this may be the result of too low a con- 

 centration rather than absence of the thioctic acid. 



In conclusion, two forms of a compound believed to be closely re- 

 lated to, if not identical with, the primary electron acceptor for those 

 electrons generated by photolysis of water in the whole green plant 

 have been isolated from barley, corn, tobacco, and Chlorella. Its var- 

 iations in the plant under changes in physiological conditions are com- 

 patible with this interpretation of its function. The compound has 

 been labeled, in Chlorella, with radioactive carbon, phosphorus, and 

 sulfur. Only the "reduced" form of the material gives a positive re- 

 action to a test for — SH groups. The compound as yet has not been 

 proved to be identical, in any way, with any known biological oxida- 

 tion-reduction carrier. 



Discussion 



Gibbs : Did you ever follow coenzyme I and coenzj^me II at the same time that 

 you were following 5a and 5b? 



Krall: Coenzyme I and II are elated at a much different place on the columns 

 than 5a and 5b. 



Gibbs: Are there changes in amomit of P'-' in tlic i)yri(liiic micleotides under 

 tliese conditiftn.s which would correspond to cliangcs in 5a and 5b? 



Krall: No, they do not show such changes. In fact there is not a good coenzyme 

 I and II peak. They would come off in eluting agent 6, if present. 



