PHOTOCHEMICAL REACTIONS 44I 



isms, there has been found vanadium-haemochromogen 

 which is also similar to bile pigments."^ 



Porphyrin derivatives are extremely widely, perhaps uni- 

 versally, distributed throughout the living world, especially 

 the iron-porphyrins which play a part in the structure of 

 living protoplasm as the prosthetic gioups of various enzymes. 

 It may be confidently asserted that there is no organism in 

 which such catalysts have been looked for and not found. 



According to Lemberg the earliest of such enzymes must 

 have been hydrogenase, which catalyses the reaction of reduc- 

 tion by molecular hydrogen based on the following element- 

 ary process^ *^: 



H. > 2H+ + 2e 



This enzyme participates in the metabolism of such typical 

 heterotrophs and anaerobes as the bacteria which carry 

 out butyric acid fermentation (Clostridia)."^ In them this 

 enzyme can only manifest its activity in the complete absence 

 of free oxygen. Hydrogenase has also been found in Esch. 

 coli,^^'^ in methane bacteria, in Azotobacter, in purple sidphur 

 bacteria and in the organisms which reduce sulphur com- 

 pounds to hydrogen sulphide."^ H. Gaffron"** established 

 that it plays a part in the reduction of cOo by green algae 

 in the dark. According to E. A. Boichenko"' this enzyme is 

 also present in the cells of higher plants. Thus we have 

 evidence of the participation by hydrogenase in the metabol- 

 ism of the more primitive anaerobic heterotrophs as well 

 as in that of chemo- and photosynthetic organisms. 



The other porphyrin-containing enzvmes are mostly cata- 

 lysts activating aerobic reactions in which free oxygen and 

 hydrogen peroxide take part. We are referring to catalase 

 and peroxidase and also to cytochromes and cytochrome 

 oxidase. 



Naturally the role of these enzymes is especially great in 

 living creatures which did not arise and develop until the 

 atmosphere of our planet had been enriched with gaseous 

 oxygen, until the respirator)^ process came into being. 



The finding of cytochrome a by M. Ishimoto and col- 

 leagues"* in the obligate anaerobe Desulfovibrio desulfiiri- 

 cans is of particular interest in this connection. It allows us 



