QUANTUM YIELD 1965 



tion. Warburg, Biirk el al. thought that when respiration is about com- 

 pensated by steady, diffuse illumination, the suspension remains for hours 

 in a state of "physiological equihbrium." They found this surmise con- 

 firmed by the steadiness of the pressure during long "dim" periods (fig. 

 37D.25J, as contrasted with changes in the rate of respiration in protracted 

 dark periods (fig. 37D.26). When cells in this state of physiological equi- 

 librium are exposed to additional, rather intense, even if locally restricted, 

 alternating illumination, it is not immediately obvious that their physi- 

 ological background will be undisturbed ; but Warburg et al. decided that 

 this is the case because they found such suspensions to return immediately 

 to the original steady compensation state after 30 or 60 min. of alternating 

 illumination. Also, they noted that the net gas exchange was the same in 

 two successive alternating illumination periods of 30 min. each (fig. 37D.25). 

 Franck suggested that this apparent steadiness is deceptive and that 

 the physiological state reached during the "dim" period, is significantly 

 altered by superimposed alternating illumination. According to Franck, 

 this superposition causes the photosynthetic apparatus to become deficient 

 in the carbon dioxide acceptor, A. Consequently, true compensation of 

 respiration, which, during the "dim" period, is achieved by normal photo- 

 synthesis with a quantum requirement of (presumably) 8 quanta per mole- 

 cule of oxygen, is replaced, during the "bright" period, by "antirespiration" 

 (photochemical reduction of half-oxidized respiration products), with the 

 same net result, but with a quantum requirement which — Franck assumed — 

 can be as low as 3, if the respiration intermediate involved is PGA (phos- 

 phoglyceric acid) or even 2 (if it is PGAP, i. e., diphosphogly eerie acid 

 containing one "high energy" phosphate bond). 



The difference between the rates of gas exchange in the dim and the 

 bright period is in this picture due to a combination of additional photo- 

 synthesis with the replacement of the part of photosynthesis that com- 

 pensated respiration in dim fight, by "anti-respiration." If the quantum 

 yield of the additional photosynthesis is calculated on the assumption of un- 

 changed background reaction, an excessively high value is obtained. 



To determine whether this quahtative interpretation is quantitatively 

 sufficient to explain results such as those shown in fig. 37D.25, the rate of 

 steady respiration and the intensity of background illumination must be 

 known; these data were not given in the paper by Warburg ei al.; Franck 

 assumed that the volume of respiration was 1.5 times the volume of cells 

 per hour (a value given in another of Warburg's papers for a similar culture) 

 and that the intensity of backgroimd light was such as to compensate this 

 respiration with a quantum yield of Vs- Applying these two postulates 

 to the extreme example of high quantum yield above the compensation 

 point, given in Warburg's paper (I/7 = 2.91, at P = 2R), Franck calcu- 



