ORIGIN AND MAI NT EN. OF OPT. ACTIVITY 51 



Krebs (11)36) proposed another interpretation of his 

 data. Following Emil Fischer's somewhat archaic views 

 on a possible synthesis in protoplasm of racemic amino- 

 acids and of their subsequent splitting into optical iso- 

 mers, he considered the deamination by a deaminase 

 specific for right amino-acids as a process by which the 

 organism decomposes the racemate and obtains the left 

 amino-acids required. But it has been seen above that the 

 experimental data available do not speak in favor of the 

 hypothesis of a primary symmetric synthesis. 



5, Biological Advantages of Optical Purity. In the 

 study of the methods used by nature to maintain optical 

 purity, some authors have considered the advantages for 

 living organisms of working with asymmetric material. 

 Mills (1932) has attempted to show that living systems 

 consisting of substances in the asymmetric state are more 

 efficient than their hypothetical racemic competitors would 

 be. On the basis of what is known on the stereo-specificity 

 of the action of, for example invertase, in the hydrolysis 

 of saccharose one can expect that the common invertase 

 activate onlv the clextrorotatorv saccharose and that the 

 optical isomer of this invertase act only on the left saccha- 

 rose. Let us consider the initial stage of the reaction, 

 when, with small concentrations of saccharose, the velocity 

 of hydrolysis is approximately proportional to the con- 

 centration of the enzyme and to the concentration of the 

 substance acted upon. In an experiment with optically 

 pure saccharose and corresponding invertase, every mole- 

 cule of saccharose coming in contact with the enzyme will 

 be subject to activation, while in an experiment with a 

 racemic saccharose and a r//-invertase only one-half of the 

 collisions will be effective. Consequently, the reaction in 

 the racemate will take place at a considerably lower rate 

 than that in the optically active system. 



It should be noticed that, in the case of two enantio- 

 morphic systems of transformations working side by side 

 (racemic material), the velocities of many processes might 

 be decreased when the two dissvmmetric substances inter- 



