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BACTERIA WITH HIGH LEVELS 

 OF SPECIFIC ENZYMES* 



Aaron ISovick 



UNIVERSITY OF OREGON 



Bacteria have the capacity to regulate over a wide range the rate at 

 which they make their various constituents. The rate of synthesis of an 

 amino acid, for example, can be varied from essentially zero to some 

 maximum rate which may be five times higher than would be needed 

 at the fastest known growth rates (Novick and Szilard, 1954). This 

 control is established by the cell in two ways : ( 1 ) by regulating the 

 rate at which an enzyme functions as catalyst of a given reaction, and 

 (2) by regulating the rate at which the enzyme itself is formed. The 

 rate of functioning of an enzyme has been found in the cases studied 

 to be controlled by the concentration of the end product of the bio- 

 chemical pathway in which the enzyme plays a role ( Umbarger and 

 Brown, 1958; Yates and Pardee, 1957). The rate of formation of an 

 enzyme appears in general to be controlled by the concentration of 

 specific repressors ( often the end product of the biosynthetic pathway ) 

 and inducers ( substrates of the enzyme ) . Apparently, when a repressor 

 is absent or when an inducer is present at saturating levels, the enzyme 

 is formed at some maximum rate (Pardee, Jacob, and Monod, 1959). 



It would be interesting to understand what determines the maxi- 

 mum rate of formation of a given enzyme, f Is the rate ultimately lim- 



" This icork was supported in part by contract ONR 2771 with the Office of 

 Naval Research, in part hij U.S.P.H.S. research grant E2H07, and in part hij 

 U.S.P.H.S. training grant 2A-14 (P.B.). 



t The rate of formation of an enzyme is defined here in rehition to the rate 

 of formation of all materials formed by the cell. In the steady state the rate of 

 formation of an enzyme defined in this way is measured by the fraction of the cell 

 represented by this particular protein. 



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