112 I. M. KLOTZ 



References 



Fredericq, E. 1954. Interactions de proteines et d'anions en solution. Arch. Internal. 



de Physiol. 62: 150-151. 

 Hughes, T. R. and I. M. Klotz. 1956. Mediation by metals of the binding of small 



molecules by proteins: Effect of hydrolytic equilibria of the metal. J. Am. Chem. 



Soc. 78: 2109-2116. 

 Klotz, I. M. and J. Ayers. Unpublished work. 

 Klotz, I. M., R. K. Burkhard and J. M. Urquhart. 1952. Structural specificities in 



the interactions of some organic ions with serum albumin. J. Am. Chem. Soc. 



74: 202-208. 

 Klotz, I. M. and W. C. Loh Ming. 1954. Mediation by metals of the binding of small 



molecules by proteins. J. Am. Chem. Soc. 76: 805-814. 

 Peticolas, W. L. 1954. Ph.D. Dissertation, Northwestern University. 



Mr. Leopold ISIay (Johns Hopkins University) : I wonder how you can ex- 

 tend the interaction between the anion and the proteins to explaining why pre- 

 cipitations occur between proteins and substances such as trichloroacetic acid. 



Professor Klotz: Essentially you have the same thing with hapten-anti- 

 body interactions. You can visualize, I think, mechanisms in which there may 

 be cross-linkages, or there may be merely cancellation of charge. Let us consider 

 trichloracetic acid with protein in an acid solution. The protein carries a plus 

 charge, which would interact with the solvent, but as these groups are covered 

 with negative charges of CI3 CCOO~ ions, the polar substituents are neutralized, 

 which decreases the ability of the protein to interact with the solvent. I think 

 that this might cause a precipitation. 



Mr. May: We made an observation with bovine serum albumin and human 

 serum albumin precipitated with trichloracetic acid. The precipitate will dis- 

 solve in 95% ethyl alcohol, methyl alcohol or acetone, whereas, the precipitate 

 with phosphomolybdic acid or some other reagents is not soluble in these non- 

 aqueous media. I wonder how these facts could be explained. 



Professor Klotz: This is, I think, implicit in what I said. In the case of 

 trichloracetic acid you would have the protein with all its plus groups holding 

 the trichloracetate anions and with the organic groups extending out into the 

 solvent, so that the organic end of the complex would suffice to get the complex 

 in solution in organic solvents. On the other hand, perhaps with the phospho- 

 molybdic acid precipitate there is a cross linkage between protein molecules 

 and the organic solvent cannot break that up (Fig. la). 



Dr. Pressman: I would like to ask one question and then make a comment. 

 First, when you vary the dielectric constant by the use of glycine, how are you 

 sure that the effect you observe is not due to a displacement of the bound sub- 

 stance by the glycine, as you indicated to be the effect of dioxane? 



Then there is probably more to the problem of charge than you have indi- 



