BIOSYNTHESIS OF UROPORPHYRIN PRECURSORS 483 



tion of uroporphyrinogen to uroporphyrin with iodine under the 

 proper conditions. 



It has been possible also to demonstrate, using slightly modified 

 conditions, the extensive conversion of uroporphyrinogen I, as well as 

 the colorless product of the action of porphobilinogen deaminase on 

 PBG, to porphyrins with fewer than eight carboxyl groups per mole- 

 cule by frozen and thawed preparations of Chlorella. The quantitative 

 extent of the conversion is the same in the case of both substrates. 

 These data, plus those given in this paper, support the conclusion 

 that the colorless product of the action of the deaminase on PBG is 

 uroporphyrinogen and most of it is of the I isomer type. 



^^^len the deaminase, a preparation of the isomerizing enzyme, and 

 PBG are incubated together under anaerobic conditions and in the 

 presence of cysteine, little or no poiphyrin appears although the 

 substrate is consumed. The incubation of this material, in which the 

 PBG is exhausted, with the frozen and thawed Chlorella leads to the 

 formation of porphyrins with fewer than eight carboxyl groups per 

 molecule, including protoporphyrin. These Chlorella preparations are 

 capable of catalyzing the production of the same porphyrins when 

 uroporphyrinogen III is supplied as the substrate. Thus the un- 

 oxidized product of the PBG-deaminase-isomerizing enzyme system 

 appears to be uroporphyrinogen III. (Also see: Neve, R. A., Labbe, 

 R. F., and Aldrich, R. A., /. Am. Chem. Soc, 78, 691 (1956).) 



Discussion 



Vernon : Have you made any models of this tetrapyrrylmethane? 



Bogorad: Well, let me say that tripyrrylmethanes of this same general con- 

 figuration have been sj^nthesized. Now, the only difference between this postulated 

 tetrapyrrylmethane and the tripyrrylmethanes which have been synthesized, 

 besides the added pyrrole, is in the side chains which would probably not inter- 

 fere stearically. Tetrapyrrylmethanes of the kind we have postulated have never 

 been seen except on paper. 



References 



1. Shemin, D., and Russel, C. S., J. Am. Chem. Soc, 75, 4873 (1953). 



2. Shemin, D., Russel, C. S., and Abramsky, T., J. Biol. Chem., 215, 613 (1955) 



3. Granick, S., Science, 120, 1105 (1954). 



4. Schmid, R., and Shemin, D., J. Am. Chem. Soc, 77, 506 (1955). 



5. Gibson, K. D., Neuberger, A., and Scott, J. J., Biochem. ./. (London). 68, nH 



(1954). 



