720 THE BIOCHEMISTRY OF B VITAMINS 



between the vinyl-containing and nonvinyl-containing porphyrins for 

 certain apoenzymes. 



The free ionizable propionic acid side chains seem to be essential for 

 biological activity of the various porphyrins. When these propionic groups 

 were esterified, none of the compounds tested either supported or inhibited 

 the growth of Hemophilus influenzae. 118 Apparently the free carboxyl 

 groups are necessary for the attachment of the iron porphyrins to the 

 basic groups of the apoenzyme. 



High concentrations of heme inhibit the growth of some bacteria or 

 even cause lysis. Cultures of Bacillus subtilis disappear 24 hours after the 

 addition of blood to the medium and their growth is completely inhibited 

 by heme in a concentration of 1 : 125,000. 133 C orynebacterium diphtheriae 

 is inhibited by even low concentrations of heme, especially under aerobic 

 conditions. 134 Lwoff m attributes these effects to the inhibition in vivo .of 

 the succinic acid dehydrogenase enzyme system by heme, a phenomenon 

 observed in vitro by Keilen and Hartree. 135 Since the biosynthesis of 

 heme occurs in these same bacteria, this may be considered an antibiotic 

 effect. Iron mesoporphyrin has also been reported to be an inhibitor for 

 many bacteria. 136 



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