SPECIFIC BINDING OF INORGANIC MERCURY TO NA-K+-ATPASE IN RAT-LIVER PLASMA-MEMBRANE AND SIGNAL-TRANSDUCTION()

Specific binding of Hg2+ to ouabain-sensitive Na+-K+-ATPase of rat liv er plasma membrane was demonstrated with a K-a of 2.64 x 10(9) and B-m ax of 1.6 nmole mg(-1) protein. The binding of mercury to the enzyme a lso causes significant inhibition of the enzyme, which is greater than its ouabain sensitivity, In the cytosol Hg2+ binding to reduced gluta thione (GSH) is stimulated by GSH-S-transferase (GST), the activity of which was found to be significantly enhanced by 15 mM Na+ and 10 mM H g2+, It is proposed that the transport of Hg2+ inside the cell takes p lace by increased dissociation of Hg2+ from the membrane due to greate r avidity of Hg2+ towards cytosolar GSH binding, The GSH-Hg complex en ters the nucleus where it dissociates to bind the metal response eleme nt (MRE) of the metallothionein (MT) gene to induce MT transcription.