Transient kinetics of oxygen dissociation from ferrous subunits of iron-cobalt hybrid hemoglobins. The principal reaction controlling the co-operativity

Keiko Kitagishi, Masao Ikeda-Saito, Takashi Yonetani

Research output: Contribution to journalArticlepeer-review

2 Citations (Scopus)

Abstract

The oxygen dissociation constants from Fe subunits in the half-ligated intermediate states of FeCo hybrid hemoglobins, α(FeO2)2β(Co)2 and α(Co)2β(FeO2)2, have been determined as functions of pH, temperature and inositol hexaphosphate. The oxygen dissociation rates from α(FeO2)2β(Co)2 are estimated to be more than 1300 s-1 for the deoxy quaternary state (T-state) and less than 3 s-1 for the oxy quaternary state (R-state) at 15 °C in 50 mm-Tris or Bis-Tris buffer containing 0·1 m-Cl-, while those of α(Co)2β(FeO2)2 are more than 180 s-1 and less than 5 s-1 for the T and R-states, respectively. The pH dependence of the oxygen dissociation rate from Fe subunits is large enough to be accounted for by the R-T transition, and implies that those half-ligated intermediate hybrids mainly exist in the R-state at pH 8·8, and in the T-state at pH 6·6, while other studies indicated that the half-ligated hybrids are essentially in the R-state at pH 7. Large activation energies of the oxygen dissociation process of 19 to 31 kcal/mol determined from the temperature dependence suggest that the process is entropy-driven.

Original languageEnglish
Pages (from-to)1119-1126
Number of pages8
JournalJournal of Molecular Biology
Volume203
Issue number4
DOIs
Publication statusPublished - 1988 Oct 20

ASJC Scopus subject areas

  • Structural Biology
  • Molecular Biology

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