690 5. OXIDANTS 



Iodine can interfere with the transport of substances across cell mem- 

 branes. Hemolysis by glycerol and other nonelectrolytes is quite potently 

 inhibited by iodine at 0.08 mM (LeFevre, 1947, 1948) as it is by various 

 SH reagents. The effects are readily reversed by thiols. This was taken to 

 indicate that SH groups are in some manner involved in the transport of 

 these substances into the erythrocytes. However, it is not necessarily evi- 

 dence for an active transport, since membrane permeability could be af- 

 fected directly or indirectly. Iodine also inhibits the transport of phosphate 

 into staphylococci and it was claimed that this process involves SH groups 

 (Mitchell, 1954). Finally, iodine at 0.1 mM reduces the short-circuit current 

 and electrical potential of frog skin (Eubank et al., 1962), but there is no 

 evidence as to the site or mechanism of this action. 



Iodine has been studied a great deal in connection with its germicidal 

 activity (Gershenfeld and Witlin, 1950) but not a great deal has been done 

 from the metabolic standpoint. The effects of pH on the ability of iodine 

 to kill bacteria, fungi, or spores are, however, of interest, since they would 

 presumably apply to work with any cells. It has generally been considered 

 that at lower pH's there is more free iodine, and hence greater penetrability 

 into cells and greater activity. It is true that more iodate would be formed 

 in alkaline solutions and, in the absence of much iodide, more hypoiodous 

 acid. Wyss and Strandskov (1945) found the bactericidal activity to de- 

 crease at higher pH's and attributed this to a greater formation of HOI 

 and lOg". When iodide is present, the formation of HOI is suppressed, and 

 the pH does not affect the activity. It was also observed, as would be ex- 

 pected, that the action of iodine is strongly dependent on temperature, re- 

 quiring about 4 times as long to kill Bacillus metiens spores for each 10° 

 drop in temperature. 



PEROXIDES 



Hydrogen peroxide and other peroxides occasionally depress enzymes and 

 metabolism potently but little is known about the specificity with respect 

 to SH groups. In comparison with other oxidants, no thorough studies of 

 the effects of hydrogen peroxide on proteins have been made. Mirsky and 

 Anson (1935) mention that hydrogen peroxide is convenient to use in the 

 oxidation of SH groups, but it has never been widely applied for this pur- 

 pose. The interesting effects of hydrogen peroxide on glycolysis and a few 

 enzymes justify a brief discussion. 



Chemistry 



Hydrogen peroxide is a nonlinear molecule that is quite miscible with 

 water: 



H2O2 + H2O -? H3O+ + OOH- K = 2Ax 10-1'' 



