Binding of beryllium and other divalent metal ions to ferritin in relation to metal requiring enzymes

Author

Daniel Jonathan Price

Date of Award

3-1983

Degree Type

Dissertation

Degree Name

Doctor of Philosophy

Major Professor

Jayant G. Joshi

Abstract

The ability of ferritin to bind various divalent metal ions (Be²⁺, Cd²⁺, Zn²⁺ and Cu²⁺) and was documented. Information obtained concerning amounts of metal bound and affinity with which they were bound was quantitated for each metal binding to ferritin or apoferritin. Enzyme activity studies were conducted to test ferritin's ability to serve as a metal donor for enzymes activated by the metal or as a metal acceptor for enzymes inactivitated by the metal.

For studies of Zn²⁺ exchange, ferritin was isolated from Cd²⁺ injected, Zn²⁺ injected and control rats. Such ferritins contained between 1-9 gram atoms Zn²⁺ (ferritin-control < ferritin-Zn < ferritinCd) . This ferritin bound Zn²⁺ was donated to Zn²⁺ requiring apo—enzyme forms of alkaline phosphatase, yeast phosphoglucomutase and yeast aldolase, resulting in the reactivation of these enzymes. Accumulation of Zn²⁺ in ferritin also suggested its role as a Zn²⁺ detoxicant for enzymes sensitive to Zn²⁺ excess.

The ability of ferritin and apoferritin to bind Be²⁺ was quantitated and compared to the binding of other divalent metal ions (Zn²⁺, Cd²⁺ and Cu²⁺). For each metal, binding affinities (K_D) and binding capacities (n) were determined. Because of the exceptional chemical properties of Be²⁺ in solution, it was necessary to use different procedures for such determinations than were used for other metals. Although the affinity of Be²⁺ for ferritin was similar to other metals (K_D ≈ 10^-6M), significantly more Be²⁺ was bound (>800 gram atoms Be²⁺ vs. < 400 gram atoms of other metals). Based on comparison of the Be²⁺ binding of apoferritin and holoferritin it was concluded that Be²⁺ was bound mainly to the iron-oxyhydroxide phosphate core. This was in contrast to the other metals (Zn²⁺, Cd²⁺ and Cu²⁺ which bound the core to a lesser extent.

It was shown that ferritin protected three Be²⁺ sensitive enzymes in vitro. These included alkaline phosphatase, Na⁺-K⁺ ATPase and rabbit muscle phosphoglucomutase. Ferritin was shown to reactivate phosphoglucomutase inactivated with Zn²⁺, Cd²⁺, Cu²⁺ or Be²⁺. Calculations were made concerning the theoretical reactivation of Zn-PGM by ferritin. A model was presented to explain the observed binding of Be²⁺ to ferritin.

Recommended Citation

Price, Daniel Jonathan, "Binding of beryllium and other divalent metal ions to ferritin in relation to metal requiring enzymes. " PhD diss., University of Tennessee, 1983.
https://trace.tennessee.edu/utk_graddiss/13120