Model compounds for the T state of hemoglobin

J. P. Collman, J. I. Brauman, K. M. Doxsee, T. R. Halbert, K. S. Suslick

Research output: Contribution to journalArticlepeer-review


O2 binding to a series of ferrous and cobaltous 'picket fence' porphyrins is reported. N-Methylimidazole and covalently attached imidazoles give O2 binding to ferrous porphyrins with ΔH° = -16.2 kcal/mol (-67.7 kJ/mol) and ΔS° = -40 eu (standard state, 1 atmosphere O2). Similar studies with cobaltous porphyrins yield ΔH° = -12.8 kcal/mol (-53.5 kJ/mol) and ΔS°= -39 eu. These values match well those of myoglobin and isolated subunits of hemoglobin and their cobalt reconstituted analogues. 1,2-Dimethylimidazole has been successfully used to mimic the presumed restraint of T state hemoglobin. In direct analogy to the decreased cooperativity shown by cobalt-substituted hemoglobin, model cobalt porphyrins show a smaller decrease in O2 affinity than the analogous iron porphyrins when the axial base is hindered. Thermodynamic data are presented. The molecular mechanism of cooperativity in hemoglobin is discussed.

Original languageEnglish (US)
Pages (from-to)564-568
Number of pages5
JournalProceedings of the National Academy of Sciences of the United States of America
Issue number2
StatePublished - 1978
Externally publishedYes

ASJC Scopus subject areas

  • General


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