II. Influence of O2 Concentration and Respiration* 



R. A. OLSON, F. S. BRACKETT, and R. G. CRICKARD, Laboratory of 



Physical Biology, National Institute of Arthritis and Metabolic Diseases, 



National Institutes of Health, Public Health Service, United States Department 



of Health, Education, and Welfare, Bethesda, Maryland 



Of the O2 transients presented in the previous paper, attention is 

 centered here on the oxygen burst and its relation to the subsequent 

 COa-hmited sustained rate. Through a study of the influence of various 

 factors, a distinct separation of the identity of these phenomena can 

 be shown. This may lead eventually to a clarification of the stepwise 

 events occurring in Chlorella following the dark-light transition and 

 their relation to respective reservoirs of metabolic intermediates. 

 This information, not available from parallel studies of steady-state 

 phenomena, should constitute a substantial contribution to the 

 analysis of the overall process of photosynthesis. 



Although concrete evidence for oxygen bursts in photosynthesis 

 has been reported previously under anaerobic or partially anaerobic 

 conditions (1-5 and others), determination of the factors which affect 

 their magnitude has not been provided because of the qualitative 

 nature of the data (1) or because of the obscuring effect of time lag 

 introduced by the presence of air-hquid interfaces (2-4) . Even in those 

 methods which overcome these difficulties (5) , the lack of derivative 

 recording and the need of manual rate determinations attenuates the 

 adequate quantitative comparison of burst maxima under various 

 experimental conditions. The reduced gain required to measure such 

 effects in aerobic suspensions offers, in this respect, even further diffi- 

 culty. The advantages of quantitative polarographic rate recording 

 are thus emphasized in the findings reported below. 



METHODS 



Cells were cultured and illuminated as described in the preceding 

 paper. Cell suspensions 0.2% were equihbrated with various gas 



* A j)ieliminai y report of this work was presented at the September 1955 meet- 

 ing of the Society of General Physiologists. An abstract is published in ./. Cellular 

 Comp. Physiol., 46, 2, 353-354 (1955). 



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