266 PROPHYRINS 



Note particularly that ring IV has been partially reduced in comparison with the hematin 

 porphyrins. The C20 alcohol esterified to one of the carboxyl groups is phytol, a diter- 

 pene. The various chlorophyll derivatives which occur naturally or as artifacts in work- 

 ing with chlorophyll involve removal of the magnesium and hydrolysis of one or both ester 

 groups. A summary of such derivatives is given in Table 2. 



Following this nomenclature, chlorophyll may be described as the phyllin of pheo- 

 phytin, phytyl chlorophyllide, etc. The letters a and b may be suffixed to any of the 

 above to denote whether a methyl or formyl group is present at position 3. An additional 

 compound in this group is protochlorophyll, which occurs in seedlings grown in the dark 

 and in seed coats of the Cucurbitaceae. Its structure is the same as that of chlorophyll 

 a except that ring IV is in the unreduced form. Magnesium-free protopheophytin may 

 also occur in some seed coats. 



TABLE 2. NOMENCLATURE OF CHLOROPHYLL DERIVATIVES 



NAME STRUCTURE 



chlorin a dihydroporphyrin 



rhodin a dihydroporphyrin with carbonyl adjacent to 



a pyrrole ring 



phorbin dihydroporphyrin with additional carbocyclic 



ring 



phorbide an ester of phorbin 



pheophorbide methyl ester of phorbin 



phytin phytyl ester of phorbin 



pheophytin methyl and phytyl ester of phorbin 



phyllin a magnesium derivative of any of the above 



chlorophyllin magnesium derivative of phytin 



chlorophyllide magnesium derivative of pheophorbide 



ISOLATION 



The metal-free porphyrins may be extracted at a pH of 2-5 using ether or ether- 

 acetic acid mixtures. The highly carboxylated uroporphyrins, however, are insoluble 

 in ether and can be adsorbed on talc or calcium phosphate gel after ether extraction to 

 remove any other porphyrins (cf. Sveinsson et al. , 9). 



There are no generally applicable procedures for the preparation of hematin com- 

 pounds from plants. Since all of them are firmly bound to protein, the procedures used 

 are those of protein chemistry rather than porphyrin chemistry. A method suitable for 

 preparing a given cytochrome from one organism may be entirely unsuited for preparing 

 the same cytochrome from another organism, or for preparing a different cytochrome 

 from the same organism. A few specific papers in this field may be cited as guides and 

 are listed on the following page: 



