NUTRITIONAL FACTORS OF DOUBTFUL STATUS 719 



and his co-workers 122 have reported that the protein moiety of horse- 

 radish peroxidase combines with protoheme, mesoheme, and deuteroheme 

 to form substances with 100, 53, and 63 per cent, respectively, of the 

 original enzyme activity. 



Since heme is known to be a constituent of oxygen-activating enzyme 

 systems, it has been generally accepted that it was indispensable only 

 for aerobic life processes. It was thought that Hemophilus influenzae, a 

 facultative anaerobe, would not require heme when grown under anaerobic 

 conditions. This view was supported by experiments of Kopp 123 and 

 Eirund, 124 but it was later shown by Gilder and Granick 119 that a small 

 amount of heme was required even for anaerobic growth. According to 

 Lwoff, 111 heme possibly functions also in enzyme systems other than 

 those concerned with the activation of oxygen. 



The nutritional requirements of some trypanosomidae were studied by 

 Lwoff and Lwoff. 111 - 115 - 117 - 125 - 126 - 127 > 128 - 129 > 13 ° These parasites, which 

 live in the digestive tubes of certain flies, could be grown on artificial 

 medium only if it contained blood. Lwoff showed that blood can be 

 replaced by either heme or the iron-free protoporphyrin in its role of 

 stimulating the multiplication and respiration of Strigomonas fasciculata, 

 but that all the nonvinyl-containing porphyrins and hemes, as well as 

 cytochrome c, peroxidase and the "active iron" of Bandisch, were in- 

 active. Hence, Strigomonas fasciculata like Hemophilus influenzae is able 

 to insert iron into the protoporphyrin molecule. 



The only insect which has been found to require heme for growth is 

 the assassin bug, Triatoma infestans. lzx ' 132 The artificially fed larvae 

 of this insect require either blood or heme in their diet in order for 

 normal growth to occur. 



In the course of their investigations Granick and Gilder 118 discovered 

 that when iron-free porphyrins were added to a medium containing either 

 protoporphyrin or iron protoporphyrin, the former substances inhibited 

 the growth of Hemophilus influenzae. The inhibition was of the competi- 

 tive type, the molecular ratio of the nonvinyl-containing porphyrin to 

 protoporphyrin at almost complete inhibition being nearly constant. The 

 molecular ratio of hemato-, deutero-, and coproporphyrin fco protopor- 

 phyrin for almost complete inhibition was approximately 10 to 1. A 

 similar competition was also observed between iron protoporphyrin and 

 other iron porphyrins. All these compounds support growth of the or- 

 ganism, but only iron protoporphyrin forms enzymes which reduce nitrate 

 to nitrite. When iron mesoporphyrin was added to a medium containing 

 a suboptimal concentration of heme, the growth of Hemophilus influenzae 

 was enhanced but its ability to reduce nitrates was decreased. These 

 observations led Granick and Gilder to conclude that a competition exists 



