LIGHT REACTIONS IN R. VANNIELH 439 



which react only to light, and (3) those which react only to oxygen. It 

 appears to be relatively deficient in the first type, and appears to have 

 roughly twice as much of the second type as of the third type (see Fig, 

 4). 



The apparent quantum requirement of 10 for cytochrome oxidation 

 in Rhodomicrobium is rather high in comparison with reported re- 

 quirements of 1 for Chromatium (10) and 3 to 4 for Rhodospirillum 

 rubruin (11), The quantum requirement for CO2 fixation in photo- 

 synthetic bacteria ranges from 9 to 12 (12,13), This corresponds 

 roughly to a maximum quantum requirement of 3 to 4 for cytochrome 

 oxidation. It is possible that the few experiments upon which the 

 quantum efficiency estimate for Rhodomicrobium are based were not 

 carried out under optimum conditions. 



ACKNOWLEDGMENTS 



Our thanks go to Dr. Sam Conti for stimulating interest and helpful discus- 

 sion. 



This work was carried out at Brookhaven National Laboratory under the 

 auspices of the U. S. Atomic Energy Commission. A portion of the work was 

 supported by Grant #G-19453 to Dr. Conti from the National Science Foundation. 



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