1788 



CHEMISTRY OF rilLOROPLAST PIGMENTS 



CHAP. 37b 



other observers, and suggest contamination of the green cells with purple ones, and of 

 tlic puii)l(' foils with green ones. 



8. Molecular Structure and Properties of Phycobilins 



(Addendum to Chapter 17, part B) 



Lemberg and Legge (1949) reviewed the data on bile pigments, in- 

 eluding the phycobilins. Structural formulae of phycoerythroljilin and 

 phycocyanobilin, suggested by Seidel (1935), are represented below in a 

 form which emphasizes their similarity to porphyrins and chlorins. 



COOHCH.CH 



HaC C2H5 



(I) Seidel's mesobiliviolin 

 ( = phycocyanobiliii ?) 



COOHCH.CH 



H3C 



C.H. 



(II) Seidel 's mesobilirhodiu 

 (, = phycoerythrobihn?) 



COOHCH,CH 



CH.CHoCOOH 



H3C 



C2H5 



(III) Lemberg and Legge's suggested 

 formula for phycoerythrobilin 



The two formulae, I and II, differ only by the position of one imino 

 hydrogen, and consequent alteration in the path of the (seven-membered) 

 conjugated double bond system. The question was raised in Vol. I 

 (p. 443) whether, in the case of porphin derivatives, arrangements of this 

 type would be stable isomers, tautomers or mesomers. In the case of 

 bilan derivatives, mesomery or tautomery is less likely, because of the open- 

 ness of the whole structure. Their isomers could therefore be stable; 

 the considerable spectroscopic difference between the two pigments makes 

 it unlikely that they are isomers containing conjugated double bond systems 

 of the same length, as implied in the formulae (I) and (II). Lemberg and 



