Bacfenal Metabolism 83 



dence that in Rhodospir ilium rubrum the cytochrome sys- 

 tem participates in the photosynthetic process, since the 

 bacterial cytochrome is reduced by organic electron donors 

 and is reoxidized by a light-generated oxidizing agent 

 through the action of a specific cytochrome photooxidase. 

 With these recent developments, a rapid extension of 

 knowledge of the nature and function of bacterial cyto- 

 chrome systems can be expected in the near future. 



Biosynfhefic Pathways 



One of the most important aspects of bacterial metab- 

 olism, to which I have scarcely referred, is the synthesis 

 of cellular constituents, such as amino acids, purines, pro- 

 teins, and polysaccharides. Since many bacteria grow in 

 simple media containing only one or a few organic com- 

 pounds, it is obvious that they possess highly developed 

 synthetic mechanisms. Time does not permit me to give 

 even a superficial account of progress and problems in the 

 analysis of biosynthetic pathways. Suffice it to say that 

 elucidation of the mechanisms of biosynthesis is a major 

 objective of current research in bacterial metabolism, and 

 it undoubtedly will receive increasing emphasis as the 

 simpler and more conspicuous problems of bacterial ca- 

 tabolism are satisfactorily solved. 



I hope this brief survey of a few aspects of bacterial 

 metabolism is convincing evidence that the subject is in 

 a state of active development. As I have tried to emphasize, 

 we are now in the midst of an attempt, started many years 

 ago, to discover the chemical mechanisms whereby rela- 

 tively simple nutrients are converted into living organisms. 

 I say "organisms" rather than "bacteria" because even for 

 microbiologists the real objective is to understand the 

 chemical basis of life rather than the peculiarities of one 

 or another bacterial species. A great deal has been learned 

 about the dynamic aspects of biochemistry by the study of 



