The reaction diagram. The diagram depicts the traditional Challenger pathway  augmented by three effects of glutathione. V 1and V 2are the velocities of the methylation steps. GSH and other reductants increase the velocity of the reduction reactions. GSH increases the activation of AS3MT. GSH conjugates and sequesters the arsenicals iAs, MMAs III, and DMAs III. Although not indicated, the half-life of GSH in reaction mixtures is taken into account. The various inhibitions of iAs and MMAs III are indicated. The kinetics of V 1 and V 2 and the functional form, U (GSH) by which GSH affects AS3MT are given in the Methods.