Model Compounds for the T State of Hemoglobin
O2binding to a series of ferrous and cobaltous ``picket fence'' porphyrins is reported. N-Methylimidazole and covalently attached imidazoles give O2binding to ferrous porphyrins with Δ H degrees = -16.2 kcal/mol (-67.7 kJ/mol) and Δ S degrees = -40 eu (standard state, 1 atmosphere O2). Sim...
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Published in | Proceedings of the National Academy of Sciences - PNAS Vol. 75; no. 2; pp. 564 - 568 |
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Main Authors | , , , , |
Format | Journal Article |
Language | English |
Published |
United States
National Academy of Sciences of the United States of America
01.02.1978
National Acad Sciences |
Subjects | |
Online Access | Get full text |
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Summary: | O2binding to a series of ferrous and cobaltous ``picket fence'' porphyrins is reported. N-Methylimidazole and covalently attached imidazoles give O2binding to ferrous porphyrins with Δ H degrees = -16.2 kcal/mol (-67.7 kJ/mol) and Δ S degrees = -40 eu (standard state, 1 atmosphere O2). Similar studies with cobaltous porphyrins yield Δ H degrees = -12.8 kcal/mol (-53.5 kJ/mol) and Δ S degrees = -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 O2affinity than the analogous iron porphyrins when the axial base is hindered. Thermodynamic data are presented. The molecular mechanism of cooperativity in hemoglobin is discussed. |
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Bibliography: | ObjectType-Article-1 SourceType-Scholarly Journals-1 ObjectType-Feature-2 content type line 23 |
ISSN: | 0027-8424 1091-6490 |
DOI: | 10.1073/pnas.75.2.564 |