NUTRITIONAL FACTORS OF DOUBTFUL STATUS 717 



zymes I or II. Olsen 116 showed that the growth-stimulating properties 

 of the X factor could be produced by heme (iron protoporphyrin), as well 

 as by hemoglobin, but that hematoporphyrin, hemocyanin, bilirubin, 

 chlorophyll, and pyrrole were inactive. He concluded that the growth- 

 promoting activity of heme was connected with its function in the per- 

 oxidase enzyme system. This conclusion was later shown to be erroneous 

 by Lwoff, who demonstrated that heme is also used for the synthesis of 

 cytochrome c m and that the growth-promoting activity and the per- 

 oxidase activity are not necessarily related. 111 



Granick and Gilder 118 > 119 - 12 °- m have investigated thoroughly the 

 specificity of heme as the growth factor X for Hemophilus influenzae. 

 They found that protoporphyrin IX could replace heme in all cases; in 

 fact, as is shown in Table 50, the iron-free compound has even higher 

 activity in some instances than heme itself. Evidence was obtained that 

 protoporphyrin IX was converted into heme by these organisms, showing 

 that Hemophilus influenzae is capable of inserting iron into the proto- 

 porphyrin ring. It was also demonstrated that peroxidase and catalase 

 enzyme systems were formed from the protoporphyrin added to the heme- 

 free culture medium. The observation that the direct addition of heme 

 to the medium was often less effective than the addition of protoporphyrin 

 was attributed to the fact that heme is quite readily destroyed by even 

 traces of hydrogen peroxide. This view was supported by the fact that 

 substances which are able to destroy H 2 2 enhance the growth of the 

 organism in the presence of the various iron porphyrins whereas they 

 do not affect the activity of the iron-free protoporphyrin. 119 Neither 

 cytochrome c nor crystalline beef catalase replaced factor X in stimulat- 

 ing the growth of these organisms. 



The iron-free porphyrins which do not contain vinyl groups, including 

 deutero-, hemato-, meso-, and coproporphyrins, do not replace proto- 

 porphyrin in promoting growth of Hemophilus influenzae. Mesoporphyrin 

 in small concentration did support growth of the "rough" Turner strain 

 but larger concentrations of the compound were inhibitory. However, 

 when these porphyrins lacking vinyl groups were converted into the 

 corresponding iron porphyrins and then supplied to the organisms, they 

 were found to support growth in seven of the ten strains tested (See 

 Table 50). These data suggest that the vinyl group is essential for the 

 insertion of iron into the porphyrin ring, but not for the growth-promoting 

 activity of the iron porphyrins. It appears that the nonvinyl-containing 

 iron porphyrins cannot carry out all the functions of iron protoporphyrin, 

 since the cultures grown on the former compounds do not possess the 

 ability to reduce nitrates to nitrites (Table 50). Also, maximum growth 

 is not always obtained in the presence of such iron porphyrins. Theorell 



