494 ANIMAL BIOCHEMISTRY 



synthesize a rather large quantity of that enzyme when the environ- 

 ment is changed. Akhough similar experiments with animals are 

 more difficult, animals seem to possess at least a limited ability to in- 

 crease the concentrations of enzymes, thus adapting themselves to 

 changing situations. The usual requirements for protein synthesis 

 must be met plus an additional need for a stimulating factor called 

 the inducer. Since the inducer is essential for the synthesis of the 

 new enzymatic material, the whole process is called induced or adap- 

 tive enzyme synthesis. 



The inducers are substrates of the enzyme, products of its catalytic 

 activity, or compounds closely related chemically to the substrates 

 or products. Though not all substrates induce enzyme synthesis, many 

 do. This arrangement makes it unnecessary for a cell to contain a full 

 measure of all the enzymes it can make. Rather the cell relies on an 

 induced synthesis of enzymes to adapt it to new environments and 

 thereby conserves the supply of amino acids. Much study of this 

 phenomenon has supported and extended the observations made with 

 the non-enzymatic proteins. Perhaps formation of this latter group 

 also depends on the presence of inducers which may be normal cell 

 constituents. Although extensively studied, the role of the inducer has 

 proved elusive. The several theories are in conflict with each other 

 and with portions of the experimental evidence. Nevertheless, study 

 is continuing on this mechanism, for many workers believe it may 

 provide the clue to the whole problem of protein synthesis. 



REFERENCES 



Biochemistry of the Ami7io Acids. A. Meister. Academic Press, New York, 1957. 



Amino Acid Metabolism. Edited by W. D. McElroy and H. B. Glass. Johns Hop- 

 kins Press, Baltimore, 1955. 



The Chemical Basis of Heredity. Edited by ^V. D. McElroy and H. B. Glass. Johns 

 Hopkins Press, Baltimore, 1957. 



Protein and Amino Acid Requirements of Mammals. Edited by A. A. Albanese. 

 Academic Press, New York, 1950. 



