MECHANISMS FOR CONTROL OF ENZYME 



SYNTHESIS AND ENZYME ACTIVITY 



IN BACTERIA 



Arthur B. Pardee 



University of California, Berkeley 



Regulation of cell metabolism will be considered here with 

 respect to a set of reactions which differ from those dealt with 

 in the preceding communications. The difference in outlook 

 stems from the use of bacteria, which can double their mass 

 in as little as eighteen minutes. This rapid growth draws 

 attention to problems of regulation of the numerous reactions 

 of biosynthesis, in contrast to problems of energy supply, 

 which are more obvious in more slowly growing cells. 



Synthetic reactions take place in a highly organized way. 

 The organization in bacteria functions as if the available 

 nutrients were utilized so as to permit as rapid a growth as 

 possible under given conditions. Bacteria grow more rapidly 

 as the medium in which they are suspended is made progres- 

 sively richer in amino acids, purines, pyrimidines, etc. ; there- 

 fore, those nutrients not supplied in the medium must some- 

 how be made at different rates, sufficiently rapid in each 

 medium to keep up with the increased demands of growth. 

 Conversely, when the medium is made less complete, the 

 rate of bacterial growth is decreased, and the reactions now 

 are adjusted to the new requirements (Novick and Szilard, 

 1954). Results such as these show that control mechanisms 

 exist for organization of metabolism. 



Control as considered here is illustrated by the following 

 quantitative example. Escherichia coli can use only glucose 

 plus a few salts, in aerobic growth, to make a multitude of 

 products. The utilization of carbon goes on in a very efficient 

 way: only small quantities of the metabolic intermediates 

 (amino acids, nucleotides, etc.) spill out of the cells or are 



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