PHOTOSYNTHETIC PHOSPHORYLATION AND THE ENERGY CONVERSION PROCESS 357 



TABLE III 



Influence of Ferricyanide (in the Absence of Chloride) on Cyclic Photo- 



PHOSPHORYLATION BY SPINACH ChLOROPLASTS AND BACTERIAL ChROMATOPHORES 



{Chromatiiim) (/iMOLES Phosphate Esterified in 30 min.) 

 (Bove, Bove, Whatley, and Arnon [103]) 



Treatment Chloroplasts Chromatophores 



Control 9-2 4-9 



Ferricyanide, i /xmole 0-5 0-4 



Ferricyanide, 2 /itmoles 0-5 o ■ 



Ferricyanide, 3 /^moles 0-5 0-4 

 Ferricyanide, 5 /^imoles, reduced by 



ascorbate* 7-2 6-2 



Ferrocyanide, 5 /(moles 9-4 5-4 



* Sodium ascorbate (5 /xmoles) was tipped in from a sidearm 15 min. after 

 the beginning of the experiment, and illumination (35 000 Lux) was then continued 

 for 30 min. 



inhibitory effect of ferricyanide resulted from the capture by this ion (in 

 its oxidized form) of electrons which would have normally travelled the 

 cyclic electron transport route (fig. 5). This conclusion was strengthened 

 by the finding that the inhibition was produced by very low concentrations 

 of ferricyanide. This would be expected if, as demanded by the hypothesis, 

 the quantity of ferricyanide needed to capture electrons from the cyclic 

 system needs only to be sufficient to leave the catalytic components of the 

 svstem in an oxidized form. 



LIGHT-INDUCED OXIDATIONS OF CYTOCHROMES 



Our theory assigns to cytochromes the role of electron carriers in 

 photosynthetic phosphorylation. The initial suggestion [13] that cyto- 

 chromes oxidized by hght may act as electron carriers in the electron 

 transport chain of photosvnthetic phosphorylation was based on the 

 observation of Lundegardh [105] that the cytochrome peculiar to chloro- 

 plasts, cytochrome / [97], is oxidized on illumination. The oxidation of 

 cytochromes on illumination has also been observed in intact algae and 

 photosynthetic bacteria by Duysens [106, 107] and by Olson and Chance 

 [108]. Of special relevance is the recent finding of Chance and Nishimura 

 [109] that, in whole Chromatium cells, a light-induced oxidation of cyto- 

 chrome C.2 is independent of temperature. This accords with the main 

 postulate of our theory [94] that the primary photochemical act in photo- 

 synthesis consists of electronic excitation and is thus independent of a 

 thermal reaction. 



