Low-temperature thermochromism marks a change in coordination for the metal ion in manganese superoxide dismutase

Mei M. Whittaker, James Whittaker

Research output: Contribution to journalArticle

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Abstract

We have observed thermochromism (temperature-dependent absorption) for anion complexes of manganese superoxide dismutase indicating a change in coordination number for the metal complex at low temperatures. The ligand field spectra for the Mn(III) ion, characteristic of five-coordination for the azide complex at 295 K, cleanly convert to spectra reflecting six- coordination at low temperature, with a midpoint for the transition near 200 K. The active site structure is temperature-dependent, a relatively rigid, distorted octahedral low-temperature Mn complex melting with dehydration (or displacement of one of the protein ligands) to form a five-coordinated complex under physiological conditions. Thermodynamic parameters for the transition estimated from van't Hoff analysis (ΔH(vH) = 5 kcal/mol; ΔS(vH) = 22 cal/mol K) are consistent with reduced chemical binding and increased fluxionality at room temperature. This thermochromism of MnSD demonstrates the existence of distinct isomeric forms of the active site metal complex, whose relative stability depends on the degree of vibrational excitation. The marginal destabilization of the six-coordinate anion complex under physiological conditions suggests that the enzyme may thermally control the stability of intermediates in a dissociative displacement mechanism for substrate binding and redox.

Original languageEnglish (US)
Pages (from-to)6762-6770
Number of pages9
JournalBiochemistry
Volume35
Issue number21
DOIs
StatePublished - May 28 1996
Externally publishedYes

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Superoxide Dismutase
Metal ions
Metals
Ions
Temperature
Coordination Complexes
Anions
Catalytic Domain
Ligands
Azides
Dehydration
Thermodynamics
Freezing
Oxidation-Reduction
Melting
Substrates
Enzymes
Proteins

ASJC Scopus subject areas

  • Biochemistry

Cite this

Low-temperature thermochromism marks a change in coordination for the metal ion in manganese superoxide dismutase. / Whittaker, Mei M.; Whittaker, James.

In: Biochemistry, Vol. 35, No. 21, 28.05.1996, p. 6762-6770.

Research output: Contribution to journalArticle

Whittaker, Mei M. ; Whittaker, James. / Low-temperature thermochromism marks a change in coordination for the metal ion in manganese superoxide dismutase. In: Biochemistry. 1996 ; Vol. 35, No. 21. pp. 6762-6770.
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