HUGO THEORELL 



These peculiar effects are likely to be explained by the fact 

 that polyvalent anions are more strongly bound to many proteins 

 than are monovalent anions, but they can be displaced by higher 

 concentrations of monovalent anions. In the same manner, 

 FMN itself is displaced from the protein by chloride ions (in- 

 creased dissociation velocity). 



The influence of the chloride ion in the absence of poly- 

 valent anions on the association velocity was studied at varied 

 pH and temperature (see Figure 4). 



Fig. 4. The value of A:i as a function of j&H in 0.4 M NaCl. • O • 0.1 

 M acetate buffer. ® (gi and OOO, 0.1 Af glycine buffer (from ref. 24). 



At alkaline reaction, 0.4 M chloride moves the part of the 

 ki curve descending above />H 9 toward lower pH. values and 

 abolishes the ki maximum at pH 9, and gives a ki following 

 a monovalent dissociation curve withpK. = 9.1. We think this 

 is a salt effect on the />K of primary amino groups attached to the 

 phosphoric acid residue of FMN. 



Complete reversibility of the reaction 



FMN + apoprotein ^ 



O.Y.E. 



ki 



requires that 



^2 _ ET 



where K is the equilibrium constant. We were able to deter- 

 mine all three of the constants separately. The values of k2 and 



288 



