REGULATION OF GROWTH AND 

 COMPOSITION OF THE BACTERIAL CELL 



B. Magasanik, Adele K. Magasanik and 

 F. C. Neidhardt 



Departments of Bacteriology and Immunology and of Pathology, 



Harvard Medical School, and Children's Cancer Research Foundation, 



Children's Medical Center, Boston, Mass. 



During the past decade most of the enzymic reactions 

 responsible for the biosynthesis of amino acids, purines and 

 pyrimidines have been elucidated. It has now become possible 

 to ask by what mechanisms the many individual pathways of 

 biosynthesis are co-ordinated with one another and with the 

 energy-producing reactions of the cell; for it is obvious that 

 growth, the orderly synthesis of protoplasm, requires a highly 

 effective integration of the anabolic and catabolic activities 

 of the cell. 



Two recently discovered control mechanisms have been 

 discussed in a preceding paper (Pardee, this symposium, p. 295) : 

 they are the inhibitory effects exerted by the ultimate product 

 of a biosynthetic sequence (an amino acid or a purine- or 

 pyrimidine-nucleotide), (1) on the action, and (2) on the 

 formation of an enzyme catalysing an earlier step of this 

 sequence. It is the first of these mechanisms which is presum- 

 ably responsible for continually adjusting the rate of synthesis 

 of the metabolic intermediates according to the demands of 

 protein and nucleic acid synthesis; the second mechanism 

 would be too sluggish for the effective control of this process. 



The significance of enzyme repression [a convenient name 

 coined recently by Vogel (1957a) for the specific inhibition of 

 the formation of an enzyme, usually by the ultimate product 

 of its action] becomes clear when we consider the ability of 

 micro-organisms to adapt themselves rapidly to great changes 



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