i90 



LIGHT AND LIFE 



E. 



08 

 06 

 04 



02 

 00 

 2 

 0.4 



e 



8 

 1.0 



CHLOROPLASTS 



XH 



CHROMATOPHORES 



I ATP <■ 



lATP . 

 2e 



.CO2+ 4H* + 4e"^ !CHjO)+HjO--, 



r 

 I 



TPN*+H* +2e"-*TPNH ' 



(cyt f)-- 



(C02+H20*lCH20)+02) 



- -Fe (CN):'+e" •» Fe (CNL'" 



H20-»02+4H''t4e"] ^ 



I 

 I 



4 YOH 



- + 



cyt Cj(Fe**)-* cyt c, (Fe''**)+e".. 



DPN*+H"^ +2e"-*0PNH 



ATP 

 2e 



t ATP 



e 



t r'OH 

 - + 



08 

 06 

 4 

 2 

 

 02 

 4 

 6 

 . 0.8 

 1.0 



Fig. 2. Comparative representation of electron transport systems and associated 

 phosphorylation sites in chloroplasts and bacterial chromatophores in terms of 

 standard electrode potentials (E' „; j>W 7, 2r)°C) of known oxidation-reduction re- 

 actions (using the chemical convention of signs). Over-all reaction of photosyn- 

 thesis expressed in electron volts. Distance from XH to YOU energy of quantum 

 of \ ^ 6700 A. equal to 1.83 ev. Distance from A'H to )'OH energy of quantum 

 of \ =: 8800 A, equal to 1.40 ev. ATP/e indicates the potential span required per 

 electron if one molecule of ATP is formed by the passage of one electron through 

 the e TS system; ATP/2e indicates the average potential span required per elec- 

 tron if one molecule of ATP is formed by the passage of an electron pair through 

 the e TS system. 



to account for the inability of tfie bacterial system to produce molecu- 

 lar oxygen is an open question. At any rate the argument presented 

 here is in line with van Niel's theory, placing the main emphasis on 

 electron flow initiated by light and considering the formation of 

 high-energy phosphate as an important phenomenon but a secondary 

 one which may or may not accompany the transport of electrons 

 generated by the light reaction. 



Stanier and coworkers (17) in a recent pid^lication have presented 

 strong evidence for the importance of light-induced phosphorylation 

 in the metabolism oi acetate by Rhodospirillum rubrum. In the 

 aijsence of carbon dioxide, acetate is converted into a polymer of 

 beta-hydroxybutyrate, ATP being required for the formation of acetyl 

 coenzyiTie A. According to Stanier et al., the hydrogens required 

 for the reduction of acetate to the level of beta-hydroxybutyrate are 

 derived from the anaerobic dismiitation of 1 mole of acetate for each 

 8 moles of acetate condensed into the beta-hydroxybutyrate polymer. 

 These investigators, however, admit that one of the four electron 



