80 



PROBLEMS IN PHOTOSYNTHESIS 



come into consideration. According to Wald (36) and Morton et al. (3), 

 rhodopsin is a compound of vitamin-A-aldehyde (retinene) with a protein, 

 i.e., a carotenoidoproteid. It fulfils the condition of a required rapid and 

 reversible change upon illumination; this is its physiological function. The 

 reaction consists in hydrogen transfer of the type alcohol ^^ aldehyde 



retinene reductase 

 vitamin A ^- DPN+ , ~ > retinene + DPNH + H 



Retinene reductase is probably identical with alcohol dehydrogenase. 

 Another carotenoidoproteid which may be of interest in this connection is 



Fig. 34. Action spectrum of the photosynthesis 

 enzyme (Warburg et al., Zschr. Naturf.). 



4000 4200 4400 4600 4800 5000 6200 



Fig. 35. Absorption spectrum of Hving Chlorella 

 (Warbui-g et at., Zschr. Naturf.). 



4000 4200 4400 4600 4800 6000 5200 



A 



ooverdin which has been studied by Kuhn et al. (32). Its prosthetic group is 

 astaxanthine which has hydrogen-transferring properties. Astaxanthine 

 occurs not only in lobster eggs but also in the green alga Hematococcus pluvialis. 

 There is, however, no evidence that this proteid, like visual purple, reacts 

 rapidly and reversibly upon illumination. 



The action of blue-green light is completely inhibited by traces of HCN 

 (1/350000 A"). Thus, it may be assumed that the reaction caused by blue- 

 green light is a heavy metal catalysis. It is well known that HCN reacts 

 with complex-bound heavy metals (e.g., hemes) and with free heavy metal 

 ions as well. In a-a'-phenanthroline we possess a substance which reacts 

 with free heavy metal ions and loosely bound complexes, but not with com- 



