Energetics of heme binding to native and denatured states of cytochrome b562

Clifford R. Robinson, Yufeng Liu, James A. Thomson, Julian M. Sturtevant, Stephen G. Sligar

Research output: Contribution to journalArticlepeer-review

Abstract

Cytochrome b562 is a four-helix bundle protein containing a noncovalently bound b-type heme prosthetic group. For the first time, energetics of heme binding to an apocytochrome were measured by isothermal titration calorimetry. The heme is tightly bound to native apocytochrome b562, with a dissociation constant (K(d)) of approximately 9 nM (ΔG°= 11 kcal mol-1) at 25 °C. Unexpectedly, the thermally denatured apoprotein is also capable of specifically binding heme with modest affinity (K(d) = 3 μM, ΔG°= 7.6 kcal mol-1). This interaction results in the dependence of holocytochrome b562 stability on protein concentration in the submicromolar range.

Original languageEnglish (US)
Pages (from-to)16141-16146
Number of pages6
JournalBiochemistry
Volume36
Issue number51
DOIs
StatePublished - 1997

ASJC Scopus subject areas

  • Biochemistry

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