CHAPTER 6 



o-IODOSOBENZOATE 



The most commonly used oxidant for enzyme SH groups at present is 

 o-iodosobenzoate because it is probably the most selective for these groups. 

 For this reason it deserves a somewhat more detailed treatment than the 

 other oxidants and a separate chapter. o-Iodosobenzoate was first prepared 

 by Meyer and Wachter (1892) and studied biologically by Heinz (1899) in 

 Germany. The early interest stemmed from the use of iodine and organic 

 iodine compounds in superficial infections. Indeed, Heinz was mainly con- 

 cerned with the administration of sodium iodide and o-iodosobenzoate to- 

 gether so that by the oxidation of the iodide it would be possible to form 

 "nascent" iodine in the tissues. Consequently there w^ere early investiga- 

 tions on the antibacterial activity (Jahn, 1914) and the effects on phagocy- 

 tosis (Arkin, 1912). The initial pharmacological study was by Loevenhart 

 and Grove (1909, 1911) at the University of Wisconsin, but the results did 

 not engender much clinical enthusiasm and, inasmuch as the actions at 

 that time were not related to any metabolic site of attack, o-iodosobenzoate 

 was little used by biochemists until it was introduced by Hellerman et al. 

 (1941) for the estimation of protein SH groups. The application to enzyme 

 characterization was slow but during the past several years it has come to 

 be one of the most useful SH reagents. It differs from the arsenicals, the 

 mercurials, and the alkylating agents in not introducing new groups or side 

 chains onto the enzymes, since it is generally believed that the primary 

 action is an oxidation of the SH groups to the disulfide state. However, the 

 use of o-iodosobenzoate, like most SH reagents, in complex systems or cel- 

 lular preparations is limited because of the number of components affected 

 and the inherent difficulty in the interpretation of the results. 



CHEMISTRY 



The structures of the different oxidation states of the iodinated benzoates 

 may be written as: 



701 



