7 Does Light Inhibit the Respiration of Green Cells?* 



By O. Warburg, D. Burk, V. Schocken, M. Korzenovsky 

 and St. B. Hendricks 



It is well known that the oxygen consumption of green cells may be decreased by 

 illumination. The light intensity at which the oxygen exchange of a given culture 

 becomes zero may be termed "compensating." Above this light intensity positive 

 evolution of oxygen gas is observed. The mechanism ofcompensationby light has 

 until now remained uncertain, but the simplest explanation is obviously the pro- 

 duction of oxygen gas by photosynthesis ; that is, since light clearly produces 

 oxygen gas above compensation it is reasonable to suppose that it also does so 

 below compensation. However, the idea, old as the science of photosynthesis, 

 still persists that light inhibits respiration per se, either anticatalytically (as 

 by inactivating respiratory enzymes), or by reducing intermediates of respira- 

 tion. If this idea were true, most computations of photosynthetic efficiency 

 would be invalidated because they have been carried out below the compensation 

 point. 



A decision on this much-discussed problem has been obtained from the follow- 

 ing type of experimentation, performed many times. In the main compartment of 

 a rectangular vessel, with two side-arms containing alkali, was placed a Suspen- 

 sion of Chlorella pyrenoidosa cells in acid culture medium (pH 4.8), with air as gas 

 phase. The vessel, attached to a manometer, was rapidly shaken and alternately 

 darkened and illuminated from below with a beam of completely absorbed red 

 light of the same intensity (— 0.25 microeinsteins/min./3 cm. 2 area) as employed 

 in simultaneous quantum efficiency determinations on aliquot suspensions by the 

 2-vessel method with 5% CO2 in air as gas phase. In the vessel with low CO2 

 pressure, negligible light action was observed, the oxygen consumption in the 

 dark and in the light being practically identical, whereas, with aliquots of the 

 same Suspension under otherwise identical conditions except for adequate 

 CO2 pressure, high efficiencies of 3 to 5 quanta absorbed per molecule of O2 

 produced were observed both below and well above the compensation point, with 

 no change in dark respiration at the widely different CO2 pressures involved 

 (see example). 



This absence of light action on respiration at low CO2 pressures may appear to 

 contradict the experience of other investigators who, since the use of manometry 

 in photosynthesis, have observed, in vessels containing alkali in side-arms or middle 

 compartments, that the respiration of Chlorella could be compensated by light. 

 The explanation for this apparent discrepancy is that such experiments were 

 carried out with too high light intensities that were not controlled quantitatively 

 by means of simultaneous efficiency determinations. Light and alkali compete for 

 the small amount of CO2 formed in respiration, so that, for every CO2 pressure, 



Aus Archives of Biochemistry 23 (1949): 330. 



