Domain specificity in metal binding to metallothionein: a circular dichroism and magnetic circular dichroism study of cadmium and zinc binding at temperature extremes

Journal Article · Thu May 05 04:00:00 EDT 1988 · J. Biol. Chem.; (United States)

OSTI ID:6925029

Stillman, M J; Zelazowski, A J

Rabbit liver Zn metallothionein-(MT) will bind cadmium readily between -26 /sup 0/C and 70 /sup 0/C. The binding reaction was monitored by recording the circular dichroism and magnetic circular dichroism spectra, in the region of the RS/sup -/ ..-->.. Cd/sup 2 +/ charge transfer transition at 250 nm, at intervals as aliquots of cadmium were added. For all temperatures, these data can be analyzed in terms of a distributed mechanism for cadmium binding when Zn-MT is used, and a domain-specific mechanism when apo-MT is used. The CD spectrum measured at -26 /sup 0/C for Cd,Zn-MT, which was made by adding excess cadmium directly to Zn/sub 7/-MT at -26 /sup 0/C, is not the same as the CD spectrum of Cd-MT prepared at room temperature from the same Zn/sub 7/-MT. Measurements of the stoichiometry of the cadmium and zinc bound to MT in the presence of excess cadmium at different temperatures indicates that below 5 /sup 0/C at least one zinc atom remains bound to the protein. The mixed metal metallothionein, Cd/Zn-MT, that always forms below 5 /sup 0/C, is characterized by a single maximum near 250 nm in the CD spectrum, rather than the derivative-shaped CD envelope that is diagnostic of the (Cd/sub 4/-S/sub 11/)/sup ..cap alpha../ cluster, which indicates that the zinc occupies a site in the ..cap alpha.. domain. Rearrangement of the bound metals to the domain-specific distribution takes place if Cd,Zn-MT, prepared at subzero temperatures, is warmed above 30 /sup 0/C.

• Research Organization: Univ. of Western, London, Ontario (Canada)
• OSTI ID: 6925029
• Journal Information: J. Biol. Chem.; (United States), Journal Name: J. Biol. Chem.; (United States) Vol. 263:13; ISSN JBCHA
• Country of Publication: United States
• Language: English

Related Subjects

550201* -- Biochemistry-- Tracer Techniques
560200 -- Thermal Effects
59 BASIC BIOLOGICAL SCIENCES
63 RADIATION, THERMAL, AND OTHER ENVIRON. POLLUTANT EFFECTS ON LIVING ORGS. AND BIOL. MAT.
CADMIUM COMPOUNDS
CONFIGURATION INTERACTION
DICHROISM
MAGNETIC CIRCULAR DICHROISM
METALLOPROTEINS
METALLOTHIONEIN
ORGANIC COMPOUNDS
PROTEINS
TEMPERATURE EFFECTS
ZINC COMPOUNDS