10 OPENING ADDRESS 



teresting theoretical propositions. Franck suggested that the long 

 wavelength pigment was likely to be oxidized more easily than the 

 rest of the chlorophyll. 



If this were truly so, it would follow that our algae might be able 

 to produce oxygen in the dark red under anaerobic conditions. Bishop 

 and I made the experiment and it turned out that an adaptation to 

 photo reduction was necessary. Anaerobic treatment was not enough to 

 make the dark red radiation efficient. I reported this at the Paris 

 meeting last summer. Of course this confirms the assumptions of 

 Kok, et al. 



If it is possible to set the entire carbon dioxide reduction machinery 

 in motion, as we have done with that part of the twin-pigment system 

 which for itself alone cannot produce oxygen, then one is tempted to 

 relegate the photolysis of water entirely to the other twin. Instead of 

 making things easy, the now popular schemes of Kok, Duysens, etc., 

 introduce, however, two problems at once— or, rather, make them 

 especially conspicuous. 



According to well-known measurements of quantum yields, photo- 

 reduction on the one hand turns out to be singularly inefficient and 

 uses at least twice or three times as many quanta as it ought to, while 

 the evolution of oxygen per se might become, in these schemes, a 

 four-quanta process. 



Instead of continuing to speculate how near or far from the double 

 primary process van Niel's photolysis may be found, we may look at 

 some of the available experiments. 



Arnon, in the Proceedings of the National Academy of Sciences, has 

 in a charming way enumerated the stages of the strip tease which have 

 followed each other for a century to get at the true first stable chem- 

 ical products of the primary process. The accent is on stable, as I 

 would like to emphasize. First there was starch. Then numerous in- 

 termediates known from the respiratory sugar metabolism. Then 

 specifically PGA, then finally ATP, And here the strip comes dan- 

 gerously close to the end, because the photochemically reduced enzyme 

 PPNR of San Pietro, now rebaptized ferredoxin, is stable only in the 

 absence of oxygen. Thus the first stable primary product appears to 

 be reduced TPN. This is also the beginning of the back flow of electrons 

 (hydrogen) which leads to phosphorylation, the only chemical energy 

 source which, according to a new generalized concept, is necessary 

 under anaerobic conditions to give us the metabolism of purple bac- 

 teria or adapted algae. 



Twenty years ago Gaffron and Rubin observed a photochemical 

 evolution of hydrogen from adapted algae when they were put in nitro- 

 gen or helium, without carbon dioxide and preferably in the presence 

 of dinitrophenol. Some time later, Kamen, Breghoff andGest discovered 

 a photohydrogen evolution which they considered as being much more 

 significant than the reaction in green algae because it was so much 



