Metabolic Pathways of Bacterial Nitrification 407 



the electron transport chain are coupled with phosphate esteri- 

 fication although their exact sites have not yet been determined. 

 It may be assumed tentatively that phosphate esterification oc- 

 curs in that part of the electron transport scheme involving the 

 action of cytochrome oxidase in view of the high positive po- 

 tential of the NO2 /NO3 system ( +0.54 volts at pH 7.0) (9a). 

 Finally, the question as to how Nitrosomonas and Nitro- 

 bacter cells obtain their reducing power, which is presumably 

 also derived from ammonia and nitrite oxidation, respectively, 

 is still untouched. Assuming that electrons provided by ammonia 

 and nitrite ultimately reach the level of pyridine nucleotides or 

 succinate, then in view of the high positive potential of these 

 substrates (viz., ammonia and nitrite) energy must be provided 

 to make possible the transfer of their electrons "uphill." Investi- 

 gation of such systems should prove to be of great importance. 



REFERENCES 



1. Aleem, M. I. H. and Alexander, M.: Cell Free Nitrification by Nitro- 



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2. Aleem, M. I. H.: The Physiology and Chemoautotrophic Metabolism 



of Nitrobacter Agilis. Doctoral thesis, Cornell University, Ithaca, New 

 York, 1959. 



3. Aleem, M. I. H., and Alexander, M.: Nutrition and Physiology of 



Nitrobacter Agilis. Appl. Microbiol, 8:80-84, 1960. 



4. Aleem, M. I. H. and Nason, A.: Nitrite Oxidase, a Particulate Cyto- 



chrome Electron Transport System from Nitrobacter. Biochem. 

 Biophys. Res. Commun., 6:323-327, 1959. 



5. Aleem, M. I. H. and Nason, A.: A Cell Free Nitrite Oxidizing System 



from Nitrobacter. Fed. Proc, 1960. 



6. Aleem, M. I. H. and Nason, A.: Phosphorylation Coupled to Nitrite 



Oxidation by Particles from the Chemoautotroph, Nitrobacter Agilis. 

 Proc. Natl Acad. Sci., 46:763-769, 1960. 



7. Aleem, M. I. H. and Nason, A.: Metabolic Pathways of Bacterial 



Nitrification. Bacterial. Proc, 1961, p. 42. 



8. Alexander, M., Aleem, M. I. H. and Engel, M. S.: Cell Free Nitri- 



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9. Anderson, J. H.: Studies of the Biochemistry of Ammonia Oxidation 



by the Autotrophic Nitrifying Organism, Nitrosomonas. Doctoral 

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 9a. Ander.son, L. and Plant, G. W. E.: Table of Oxidation-Reduction 

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