RESPIRATORY HEMATIN ENZYMES 



651 



hence chlorophyll, or at least bacteriochlorophyll, preceded the 

 development of the respiratory catalysts of the hematin series. 

 Catalase is, however, present in purple bacteria (GaflFron, 968), 

 though photocatalase is lacking. It is, therefore, possible that bac- 

 teriochlorophyll and catalase appeared simultaneously. 



Certain chemical relationships can be pointed out which may have been 

 of evolutionary significance. Bacteriochlorophyll is related to chlorophyll a 

 in a way which may be expressed by: 



PoH4(COCH3)^C2H5) 

 Bacteriochlorophyll 



PoH2(C2H3)(C2H5) +H2O 



Chlorophyll a 



where Po signifies the porphyrin nucleus, and where only two side chains are 

 shown. It is not impossible that chlorophyll a has evolved from bacterio- 

 chlorophyll by a dismutation, two atoms of hydrogen being transferred from 

 the tetrahydroporphin nucleus to the acetyl side chain. Fischer and Bub 

 {806) have observed such hydrogen transfers between nucleus and side 

 chain in chlorophyll derivatives under the influence of hydriodic acid in 

 vitro. Similar dismutations may have been of importance in the conversion 

 of chlorophyll to hematin compounds, such as catalase, or inversely hematin 

 into the former, or in their origin from a common precursqr. Protoporphyrin, 

 for instance, has in its nucleus two hydrogen atoms less than chlorophyll a 

 and also two less in its second vinyl group (ethyl in chlorophyll), but the 

 opening of the isocyclic ring in chlorophyll (with formation of the second 

 propionic acid side chain of protoporphyrin) requires the addition of six 

 hydrogen atoms. This relation can be written: 



^ 



PoH. < 



C2H3 

 C2H5 



\ 



HC CO 



I 

 CO2H 



/ 



+ 2H 



Po< 



C2H3 

 C2H3 



\ 



H.C CH, 



1^ CO2H 



+ H2O 



4. RESPIRATORY HEMATIN ENZYMES 



As soon as photosynthetic organisms developed with the capacity 

 to use water as hydrogen donor for the assimilation of carbon dioxide 



