382 RESPIRATORY METABOLISM 



for or against the idea that both dehydrogenase and glutathione are part 

 of the same respiratory chain. 



5. SYNTHESIS OF RESPIRATORY ENZYMES VITAMINS 



After we have determined that a certain organism has a certain type of 

 respiratory system, the question arises of how the enzymes are formed. 

 Is the organism capable of synthesizing them from relatively simple 

 compounds, or must certain prosthetic groups be present in the nutritive 

 substrate? For certain flagellates this question has been answered very 

 definitely by A. Lwoff ( 1933) . Strigonionas oncopelti, S. jasckulata, and 

 Leptomonas ctenocephdi have respiratory systems which are 90 percent 

 dependent upon cytochrome (as demonstrated above with KCN and 

 CO). It was found that S. oncopelti could live indefinitely in peptone 

 solutions without the addition of hematin compounds. For the other 

 two flagellates, hematin compounds were found to be necessary. L. 

 ctenocephdi would not grow unless rabbit blood (or an equivalent 

 amount of hematin) were present in concentrations of one part to 1,200. 

 S. jasciculata showed growth in blood dilutions as great as 1/1,000,000, 

 and within limits the amount of growth was directly proportional to the 

 amount of blood. Hemoglobin disappeared rapidly from the culture 

 medium, and it apparently was being used to form more respiratory 

 enzyme. When small amounts of blood were added, the Qo^ increased 

 linearly for several hours, until apparently all of the hematin was con- 

 verted into respiratory enzyme; then the Q02 remained constant. This 

 constant level varied with the amount added. It was found that for each 

 gamma of blood (between one and 5 gamma) added to 1 mgm. of 

 flagellate (dry weight) the Qoo was increased about 3 units. After 8.5 

 hours 5 gamma of blood raised the Qo. from 19-5 to 37.0. Blood could 

 be replaced with hematin, prohemin, and protoporphyrin, but not by cyto- 

 chrome C nor by a wide variety of synthetic hematin and porphyrin com- 

 pounds, chlorophyll, peroxidase, or active iron (Lwoif, 1938). Ap- 

 parently only the porphyrin compound which contained the vinyl (-CH 

 = CHo) radical (protoporphyrin) was effective. Deuteroporphyrin, 

 which differs from protoporphyrin in having hydrogen in place of the 

 vinyl groups, was not effective. More recent investigations of the chem- 

 ical structure of cytochrome indicate that the vinyl groups may be neces- 

 sary for linking the prosthetic group (iron porphyrin) to the protein 



