Photosynthesis 



399 



provided is not marked, one cannot expect that more marked O2 will be consumed 

 in light than in darkness, since in light, on spatial grounds, the unmarked O2 

 photosynthetically produced within the cells will be consumed more rapidly than 

 the externally available marked O2 that must diffuse into the cells. Brown 23 found, 

 in fact, that in light there was no increase in marked respiration, but often even 

 a decrease of marked respiration; that is, not only the light respiration but also the 

 dark respiration favored the unmarked oxygen produced within the cells photo- 

 synthetically from unmarked photolyte. This is a beautiful example of "isotopic 

 discrimination." 



The light respiration during illumination has also been the object of attempted 

 measurement elsewhere, for example by Weigl, Warrington and Calvin 24 , who 

 illuminated green cells in marked CO2 and expected that in light unmarked CO2 

 would be given off in increasing quantity. They found, however, no increase in 

 unmarked CO2, quite in agreement with our equations, from which it follows that 

 the light respiration must be marked when the CO2 is marked. 



In fact, the light respiration can only be measured as it was first discovered 4 : 

 when it is separated in time from O2 development 25 , 26 . 



References and Notes 



1 Warburg, O., Schröder, W., Gattung, H., Z. Natur- 

 forsch. IIb (1956), 654. 



2 Warburg, O., Krippahl, G., Schröder, W., Z. Natur- 

 forsch. 10b (1955), 631. 



3 Warburg, O., and Schröder, W., Z. Naturforsch. 12b 

 (1957), 716. 



4 Burk, D., and Warburg, O., Naturwissenschaften 37 

 (1950), 560; Z. Naturforsch. 6b (1951), 12. 



5 Warburg, O., et al., Z. Naturforsch. 9b (1954), 769. 



6 Warburg, O., and Krippahl, G., Svensk Kern. Tidskr. 

 69 (1957), 143. 



7 Warburg, O., and Krippahl, G, Z. Naturforsch. IIb 

 (1956), 718; 13b (1958), 63. 



8 Warburg, O., Klotzsch, H., Krippahl, G., Natur- 

 wissenschaften 44 (1957), 235; Z. Naturforsch. 12b 

 (1957), 266; 12b (1957), 481; 12b (1957), 622. 



9 Here bolometry, introduced by the American physicist 

 S. P. Langley, was developed and adapted to photo- 

 chemistry by Lummer and Kurlbaum. It was Lum- 

 mer's bolometer that played a decisive role in the dis- 

 covery of light quanta. It was the bolometer of Lum- 

 mer and Kurlbaum that was used to measure light en- 

 ergy in the experiments of Emil Warburg that laid the 

 foundation of quantitative photochemistry. It is the 

 same bolometer that has now solved the problem of the 

 energetics of photosynthesis [F. Kurlbaum, Wiede- 

 mann's Ann. Physik 65 (1898), 746; O. Lummer and 

 E. Pringsheim, Verhandl. deut. physikal. Ges. 1 

 (1899), 23; 2 (1900), 163; M. Planck, ibid. 2 (1900), 

 237; E. Warburg et al., Ann. Physik 40 (1913), 609; 

 E. Warburg and C. Müller, ibid. 18 (1916), 245; 

 E. Warburg, Z. Elektrochem. 27 (1921), 135]. 



10 Franck, J., and Gaffron, H., Advances in Enzymol. 

 1 (1941), 200. 



11 Ehrmantraut, H., and Rabinowitch, E., Arch. Bio- 

 chem. 38 (1952), 67. 



12 Warburg, O., Biochim. et Biophys. Acta 18 (1955), 

 163. 



13 Emerson, R., and Arnold, W., J. Gen. Physiol. 16 

 (1932), 191. 



14 Warburg, O., Biochem. Z. 100 (1919), 230; O. War- 

 burg and Negelein, E., Biochem. Z. 202 (1928), 202; 

 214 (1929), 64. 



15 Burk, D., Cornfield, J., Schwartz, M. ; Sei. Monthly 

 73 (1951), 213. 



16 Burk, D., Federation Proc. 12 (1953), 611. 



17 Emerson, R., and Lewis, C, Am. J. Botany 26 (1939), 

 808; 28 (1941), 789. 



18 Rüben, S., and Kamen, M., J. Am. Chem. Soc. 62 

 (1940), 3451. 



19 Warburg, O., and Negelein, E., Biochem. Z. 110 

 (1920), 66. 



20 Warburg, O., and Krippahl, G., Z. Naturforsch. 10 b 

 (1955), 301. 



21 Allen, F., Arch. Biochem. 55 (1955), 38. 



22 Hill, R., and Whittingham, C, New Phytologist 52 

 (1953), 133. 



23 Brown, A., Am. J. Botany 40 (1953), 719. 



24 Weigl, J., Warrington, P., Calvin, M., J. Am. 

 Chem. Soc. 73 (1951), 5058. 



25 Reprints of this article may be obtained from the 

 translators. A general review monograph, "Problems 

 in Photosynthesis", by W. Bladergroen, will appear 

 later in the year (Thomas, Springneid, 111.). 



26 Note added in proof. Further studies clarifying the 

 mechanism of Hill reactions are in press: O. Warburg 

 and G. Krippahl, "Hillreactionen" and "Weiterent- 

 wicklung der manometrischen Methoden"; O. War- 

 burg et al., "Oxygenase in Chlorella", Z. Naturforsch. 



