Evidence for oligomerization of metallothioneins in their functional state

Capillary zone electrophoresis in the polyacrylamide-coated capillary was used to study metallothionein (MT) isoforms at physiological pH in horse kidney and rabbit liver MT preparations produced commercially by Sigma. Evidence is put forward that MT develops oligomers or aggregates in its metal binding situation at these pH values in both species. For the horse kidney preparation two forms were found for both the MT-IA and the MT-IB forms, for the rabbit liver three forms could be seen for the MT-I form and two for the MT-II form. At pH values above the physiological range (pH 8–10) up to four forms could be seen for the MT-I form (MT-IA in the horse) in both preparations. Compared to the MTCd-II form, the rabbit liver MTZn-II form not only behaved electrophoretically identical, but also showed a corresponding oligomerization behaviour. Our results indicate that the oligomerized MT-I form in the rabbit liver and the MT-IA form in the horse kidney bind more Cd atoms than the expected number of 7 per monomer.