Porphins vinyl groups

In the protoporphyrins, the eight carbon atoms of porphin carry two vinyl groups, four methyl groups and two propionic acid groups. One of the fifteen possible isomers oif this structiure is protoporph3rrin IX or porphin-l 3 5 8-tetramethyl-2 4-divinyl-6 7-dipropionic acid, commonly called protoporphyrin. This is the porphyrin most widely distributed in nature, it is a constituent of haemoglobin, catalase, peroxidase, of cytochrome-6, etc. Diuing the course of putrefaction protoporphyrin loses its unsaturated side chains and is transformed into deuteroporphyrin III. On the other hand, it can be derived by a series of operations from copro-porphyrin III, another proof of its chemical kinship with the porphyrins of Series III. 

Chlorocruorin, which acts as an oxygen carrier in certain types of Annelids, is a derivative of chlorocruorohaem. This latter substance is the haem of chlorocruoroporphyrin or Spirographis-porphyrin (from the name of the worm (Spirographis) whose blood is most commonly used as a source of chlorocruorin) (porphin-l,3,5,8-tetramethyl-2-formyl-4-vinyl-6,7- propionic acid). In fact, it is derived from protoporphyrin by oxidation of the vinyl group at position 2. 

In Hemophilus influenzae there is evidence that an iron porphin containing vinyl groups is needed for the reduction of nitrate to nitrite (54), and Quastel has reported that nitrate reduction by bacteria is affected by carbon monoxide (103a). 

H, influenzae grew on non-vinyl-containing iron porphins. However, H. influenzae when grown on the vinyl-containing porphin possessed the ability,to reduce nitrate to nitrite and it lacked this ability when grown on any iron porphin lacking vinyl groups. 

It has been noted above that porphins lacking either the iron or the vinyl groups do not support the growth of smooth strains of Hemophilus influenzae. Indeed, they actually inhibit the growth which is supported by iron porphins. A competitive inhibition of growth is readily recognized between the iron porphin (for example, iron protoporphin) and the porphin into which iron cannot be inserted (for example, deuteroporphin). 

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