PORPHYRINS 



11 



And there are six other ways in which the two water molecules might 

 be included on similar lines. Each of the bodies so formed is not only 

 a porphyrin but a hsematoporphyrin. So that there are eight slightly 

 different bodies all of which are obtained by the hydration of two 

 groupings in the protoporphyrin (ooporphyrin) and are isomeric forms 

 of haematoporphyrin. 



In point of fact hsematoporphyrin, as we know it, is probably a 

 mixture of the whole eight substances, each of which differs so slightly 

 from its fellows as to be scarcely distinguishable as a separate unit. 

 But there are other porphyrins, coproporphyrin for instance which 

 has the formula 



CH-CHiCOOH 

 z z 



HOOC-CH-CH^' '-CHj HOOC-CH-CH£ 



CH, 



and uroporphyrin 

 CH 



/COOH 

 CHCH CH, 



TOOH 



-CH-CH^ 



COOH 



HOOC 



HOOC 



\ 



CH-CHr 



-CH 



HOOC 



/H-CHj 

 HOOC 



COOH 



-CH, 



Two questions naturally arise: (1) Is it possible to make hsemo- 

 globins corresponding to porphyrins other than protoporphyrin ? and 

 (2) Do any such forms of haemoglobin occur in nature? 



