Physical-Chemical Aspects of Synthetic Auxins 301 



mitting the establishment of dipole or Van der Waal forces 

 where adsorption may be involved. 



(5) Water solubility appears to provide a natural limit to the 

 behavior of these compounds. The demonstration of the ad- 

 sorption of these compounds by proteins and by mitochondria. 



(6) The change in structtire of the peroxidase molecule. 



These observations suggest that adsorption and consequent modi- 

 fication of protein structure may be the basic action of plant growth 

 regulating phenoxyacetic acids. It may be inferred that not all en- 

 zymes or proteins are going to adsorb the chemical with equal facility 

 and, therefore, there will be a marked difference among enzymes as to 

 the response to the chemical. Likewise, the same enzyme derived from 

 different sources would quite likely have different affinities for the 

 chemical and, therefore, would show a different response in terms of 

 change of enzymatic activity. This in part may help to account for the 

 selectivity of these chemicals. 



ACKNOWLEDGMENTS 



The authors wish to acknowledge their indebtedness to F. J. Wit- 

 mer for assistance in obtaining the infrared spectra and to R. E. 

 Hughes for assistance on certain of the enzyme assays. 



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