TRANSIENTS IN ACID PRODUCTION 453 



following acid uptake seem to be closely related processes. Any 

 explanation of the former should also account for the latter. 



The quantum yield of the gush appears to be high both in algae and 

 in bacteria. The measurements of Emerson and Lewis (4) indicate a 

 quantum yield of 0.8 or higher. Although the absolute quantum yield 

 of the bacterial acid gush has not been measured, it has been found 

 that at rate-limiting light intensities the rate of CO2 (or other acid) 

 production for the acid gush is four to six times higher than the rate 

 of CO2 reduction with H2 as H-donor. This indicates that the maxi- 

 mum quantum yield (CO2 or H+ produced/quantum) of the acid gush 

 is probably in the neighborhood of V2, since most measurements of the 

 maximum quantum yield for photoreduction indicate values of Vio to 



Vs. 



The CO2 gush studied by Emerson and Lewis in algae shows a 

 dependence on oxygen which is not shared by the acid gush of Chro- 

 matium, which has normally been examined under the same strictly 

 anaerobic conditions which are required for growth of this organism. 

 The effect of oxygen is probably not specific for the CO2 gush, since it 

 is well known that photosynthesis in Chlorella is also markedly in- 

 hibited by prolonged anaerobiosis under the acid conditions ob- 

 taining in the experiments of Emerson and Lewis. 



The CO2 gush in algae requires a rather high partial pressure of 

 CO2 — a fact which suggested to Emerson and Lewis (4) and Franck 

 (5) that some sort of reversible carboxylation is involved. If the 

 P (CO2) is lowered to 0.5% the CO2 gush falls to a negligible value. 

 The acid gush in Chromatium, on the other hand, does not seem to be 

 similarly affected by the CO2 pressure since it still is of a significant 

 size at a CO2 pressure which is so low (less than 0.02%) that photo- 

 reduction is reduced to compensation of fermentation reactions. 



The data on hand do not rule out the possibility that the gush both 

 in bacteria and in algae is caused by the production of an acid other 

 than CO2 which displaces CO2 from a bicarbonate reservoir in the 

 cell. This would presuppose an intracellular bicarbonate concentra- 

 tion, under some conditions, of at least 0.009 M to explain the largest 

 acid gushes which have been observed. It may prove possible to test 

 this hypothesis by a direct measurement of intracellular bicarbonate 

 levels. 



The experiments of Emerson and Lewis (4) exclude the possibility 

 that the COj gush in Chlorella is due to the excretion of a strong acid 



