734 



7. MERCURIALS 



in serum, 126 mM in Krebs-Ringer bicarbonate medium, 143 mM in Tyrode 

 solution, 154 mM in physiological saline, and 515 vaM in sea water. The 

 distribution between species of complexes for three situations (low, moder- 

 ate, and high Cl~) is shown in Table 7-3, and the distribution over a com- 

 plete spectrum of Cl~ concentrations is illustrated in Fig. 7-1. It so happens 



Fig. 7-1. Curves showing the distribution of the different chloride com- 

 plexes of Hg++ with Cl^ concentration. (From Sillen, 1949.) 



that, in most media used in ceU and tissue preparations, the concentrations 

 of HgClg, HgClg", and HgCl4= are roughly equal, whereas in sea water the 

 predominant form is HgCl4=. In the media for isolated enzyme study, in 

 which Cl~ is often low, the predominant form may be HgClg or even HgCl+. 



Table 7-3 



Distribution of Mercuric Chloride Complexes as Fractions 

 OF the Total Mercury in Media of Different CI" Concentration 



Fraction 



(C1-) = 1 ml/ 



Krebs-Ringer medium 

 (C1-) = 126 mM 



Sea water 

 (C1-) = 515 mM 



It has often been assumed in the past that the mercuric ion Hg++ is the 

 predominant form or the active inhibitor, but it is now realized that this 

 is not the case. The importance of such complexes in inhibition studies is 

 2-fold. In the first place, the equilibria for the binding of mercury to SH 



