Kinetic studies of the reactions of isolated alpha- and beta-domains of rabbit liver MT-II with DTNB (5,5'-dithio-2,2'-dinitrobenzoic acid) and AuSTm (aurothiomalate, Myochrysine) were carried out in 5 mM Tris . HCl/0.1 M KCl at pH 7.4 and 25 degrees C. These results demonstrate that the kinetics of the DTNB reaction with the beta-domain are monophasic, with observed rates similar to those of the slow step of the reaction of the hole-protein, Cd7MT, which confirms previous findings that the alpha-domain is the site of the kinetically fast step. DTNB concentration dependence studies resulted in the following rate law, rate = {k(1s) + k(2s)[DTNB]}[MT], that corresponds to two of the four terms in the holoprotein rate law, those of the slow step. The reaction of aurothiomalate with the beta-domain is independent of the AuSTm concentration and described by a rate function with a single rate constant, rate = k(1s)[MT]. The alpha-domain reaction with AuSTm, also AuSTm-concentration independent, involves slow and fast phases with rate = {k(1s) + k(1f)}[MT]. The latter dominates 87 +/- 3% of the reaction. Comparison of these results with previous studies of other electrophiles demonstrate that the kinetically preferred reaction of MT with an electrophile may be localized in either the alpha- or the beta-domain, depending on the specific attacking reagent.