Inhibition of camel lens zeta-crystallin/NADPH: quinone oxidoreductase activity by chlorophenols

Chlorophenols comprise a major class of environmental contaminants. They are extensively used as insecticides, fungicides, mold inhibitors, antiseptics and disinfectants. We found some of these compounds to be strong inhibitors of zeta-crystallin. This oxidoreductase enzyme was isolated from camel lens and its enzymatic activity was inhibited by the chlorophenols tested in a time-independent but concentration-dependent manner. 2,4,5-Trichlorophenol was the most potent inhibitor (IC50 = 3 microM; Ki = 3.2 microM) whereas 4-chlorophenol was the least potent (IC50 = 4.1 mM). There appeared to be a relationship between the degree of chlorination of the phenols and inhibition of zeta-crystallin activity. The position of the chlorine substituent on the phenol may also influence the potency of these compounds.