CHAPTER 7 



MERCURIALS 



The mercurials occupy a rather special niche in the subject of enzyme 

 inhibition; they are very useful for demonstrating the presence and impor- 

 tance of SH groups in enzyme reactions, but apparently lack specificity 

 toward particular enzymes or classes of enzymes. Since so many enzymes 

 contain reactive SH groups at or near the active center, the mercurials 

 would seem to inhibit more enzymes than they leave unaffected. When a 

 mercurial acts on living cells, one cannot state which enzymes are affected 

 most readily. In other words, they are reasonably specific with regard to 

 the molecular group attacked, but quite nonspecific at the enzyme or cel- 

 lular levels. The mercurials wiU, in addition, react with nonenzymic proteins 

 and may modify complex systems by mechanisms unrelated to metabolism. 

 The mercurials are thus at present generally useless as tools to study the 

 relationship of a particular enzyme to the over-all metabolism, growth, or 

 function of a cell or organism. Nevertheless, with judicious use, they may 

 give some insight into the broader metabolic basis of function, as in certain 

 studies of gastric acid secretion, renal transport, and mitosis. Their primary 

 use, however, is the detection and titration of SH groups on enzymes. 

 They are often stated to be the most specific SH reagents; this may be 

 questioned, but without doubt they are among the most reactive reagents 

 and seldom does one find SH groups resistant to the mercurials and capable 

 of reacting with other SH reagents. Like all inhibitors, they are valuable 

 only when used in the proper system. It is always tempting to use inhib- 

 itors such as the mercurials which will almost always produce definite 

 effects, but unfortunately the results usually cannot be interpreted satis- 

 factorily. We shall emphasize the quantitative side of mercurial action and 

 the inhibitions of pure enzymes, discussing only briefly effects observed on 

 complex systems, inasmuch as little useful information can be derived 

 from this latter work. 



The medical use of the mercurials can be traced back for over 3000 years, 

 although their modern therapeutic applications began with the rediscovery 

 of the diuretic action of mercurous chloride in 1849 (since then this action 

 has been rediscovered several times), the demonstration of the antiseptic 



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