Biphasic reactions of DTNB with lobster Cd6- and Cd5Cu-metallothionein-2 which have two type-B (M3S9) clusters

Lobster metallothionein (MT), which has two three-metal clusters instead of the four-metal and three-metal clusters found in mammalian MTs, was used to determine the origin of the biphasic reactions of MT with DTNB. Cd-rich MTs (CdsCu-MT-2 and Cd 6 -MT-2) were isolated from lobster hepatopancreas after Cd treatment preceded by dexamethasone injection or an applied stress. Each lobster MT-2 preparation reacts biphasically with DTNB [5,5'-dithiobis(2-nitrobenzoic acid)], as do mammalian MTs, and the reaction proceeds about 1 order of magnitude easter than that of mammalian MTs