Physical-Chemical Aspects of Synthetic Auxins 305 



and to algae and a few other organisms and not about processes that 

 are common to all living things. For example, one of the lessons of 

 comparative biochemistry is that mitochondria are very much the 

 same in all living creatures. We all have the same kind of mitochon- 

 dria, and I would think that, for example, if 2,4-D or lAA did its work 

 on mitochondria, it ought then to work on all kinds of organisms. And 

 it seems to me that the hypothesis that auxins exert their effects by 

 general and nonspecific adsorption to enzymes breaks down in the 

 face of the facts of comparative biochemistry. 



Dr. Freed: Your points are well taken, Dr. Bonner. Now I call 

 your attention to the following: 



(A) It is known that a given enzyme isolated from different tissues 

 will have slightly different substrate specificities yet catalyze the same 

 essential reaction. This indicates that we are dealing with a popula- 

 tion of molecules, some of which may give a remarkable response to 

 a given chemical and still others of the same population give only a 

 slight response. Thus the problem is one of degree rather than an all 

 or none effect. This appears to arise from the differences in the struc- 

 ture of the protein. Such variation at the molecular level may account 

 in part for the variation among different organisms in their response 

 to lAA. However, one of the consequences of this postulate is that 

 many organisms may be responding to lAA but either so slightly or 

 in such a manner that we have not yet observed the response. 



(B) In support of the foregoing it must be remarked that the first 

 demonstration of the ability of 2,4-D to inhibit oxygen uptake by 

 mitochondria was performed with mitochondria isolated from animal 

 tissue rather than from plants. 



(C) Finally, it should be noted that lAA has recently been found 

 to have a marked effect on certain functions of mammalian metabo- 

 lism. Thus, Mirsky and his coworkers (Endocrinol. 59: 369. 1956) have 

 found lAA to function as an antidiabetic agent in mammals. 



It thus appears that compounds may affect a wider range of or- 

 ganisms than previously suspected. This would seem to be compatible 

 with the theory advanced. 



Dr. Leopold: It is very exciting to think that adsorptive features 

 of auxins might be relevant to their activities in biological systems. 

 We have, like Dr. Freed, been very much taken by this possibility 

 and have done some measurements of the influences of molecular 

 structure on adsorption of auxins onto charcoal. This system suffers 

 from its lack of biological specificity, to be sure, but it might tell us 

 something about the influence of molecular structure on a simple 

 adsorptive function. We found that compounds showing the great- 

 est activity as auxins also showed the greatest adsorption onto char- 



