398 Photosynthesis 



In 1955 we found 20 that one can replace the nitric acid by ferricyanide : 



(Dark) 4Fe 3 + -f C + 2H 2 = 4Fe 2 + - 4H- - C0 2 



(Light) CO-2 = C + 2 



(Balance) 4Fe 3 + - 2H 2 = 4Fe 2 + + 4H+ 2 . 



Both reactions, with living Chlorella, appear in the balance as though water 

 were decomposed by light, and as though the oxidizing agent acted only as a hy- 

 drogen acceptor, whereas in reality the light reaction is ordinary photosynthesis. 



If, in the experiments with living Chlorella, one Substitutes quinone for the 

 nitric acid or the ferricyanide, CO2 cannot participate in the development of O2, 

 since quinone completely inhibits the Splitting of CCK Likewise, with green grana, 

 CO2 cannot participate in the development of O2 since illuminated green grana 

 are unable to reduce CCK 



One must therefore either postulate two different mechanisms of photochemical 

 O2 development in green grana and in intact cells, which is improbable, or one 

 must attempt to find a common explanation for the two phenomena: for water 

 decomposition with intermediate photosynthesis, and for water decomposition 

 without intermediate photosynthesis 6 . 



7) The experiments ofF. W. Allen. In order to test whether photosynthesis without 

 O2 is possible, Allen 21 , at the Suggestion of James Franck, made use of the fact 

 that the phosphorescence of many dyes is diminished by traces of O2. A stream of 

 nitrogen containing CO2 was conducted over glowing copper, from there over 

 water, then over a Suspension of Chlorella, over liquid nitrogen, and finally over 

 the dye acriflavin adsorbed on silica gel. Allen still found detectable photosyn- 

 thesis at an O2 pressure of 10~ 6 mm-Hg; whereas our manometry in closed vessels 

 showed, without possiblility of error, that below 10 ^ mm-Hg photosynthesis in 

 Chlorella is very small. What is the meaning of this discrepancy of five powers of 10 ? 



The method of James Franck must be calibrated empirically — that is, each O2 

 pressure yielding a given phosphorescence must be analytically determined. 

 Furthermore, O2 pressures of the order of magnitude of ICH' mm-Hg must be 

 produced, maintained, and analytically measured in a rapidly flowing gas. Anyone 

 who is accustomed to performing experiments himself knows that this is an almost 

 insoluble task. In any event, the analytical determination of traces of O2 is the key 

 aspect to the Franck method, and since Allen himself remained silent about this 

 point, one must seek the mistake here. The calibration was obviously false by five 

 powers of 10. 



On the other hand, experiments of Hill and Whittingham 22 agree very well 

 with our results. These workers added reduced hemoglobin to a Suspension of 

 Chlorella and determined the 02-development upon illumination by optical 

 measurements of the resulting oxyhemoglobin. They found that photosynthesis 

 already began to fall off at an O2 pressure of about 2 mm-Hg. 



8) The experiments of Allan Brown on „light-respiration.' n When the light reaction 

 and the dark reaction oberlap in photosynthesis under normal conditions, two- 

 thirds of the O2 developing in the light will be reabsorbed so rapidly that. one can 

 think of the oxygen as oscillating between the free State and a binding with carbon. 

 If the molecular O2 provided the Chlorella is isotopically marked, whereas the CO2 



