Model compounds for the T state of hemoglobin.
O2 binding to a series of ferrous and cobaltous "picket fence" porphyrins is reported. N-Methylimidazole and covalently attached imidazoles gives O2 binding to ferrous porphyrins with deltaH degrees =-16.2 kcal/mol (-67.7 kJ/mol) and deltaS degrees =-40 eu (standard state, 1 atmosphere O2). Similar studies with cobaltous porphyrins yield deltaH degrees =- 12.8 kcal/mol (-53.5 kJ/mol) and deltaS 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 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.
D003035:Cobalt; D006454:Hemoglobins; D007501:Iron; D008956:Models, Chemical; D009211:Myoglobin; D010100:Oxygen / Q000097:blood; D011166:Porphyrins / Q000378:metabolism; D011485:Protein Binding
D006454:Hemoglobins; D009211:Myoglobin; D011166:Porphyrins; D003035:Cobalt; D007501:Iron; D010100:Oxygen
J Am Chem Soc. 1977 Aug 17;99(17):5628-32
886121
Proc Natl Acad Sci U S A. 1977 Mar;74(3):801-5
265575
J Mol Biol. 1977 Jan 5;109(1):83-97
14263
J Biol Chem. 1977 Jan 25;252(2):620-4
188820
Proc Natl Acad Sci U S A. 1977 May;74(5):1789-93
266703
Br Med Bull. 1976 Sep;32(3):195-208
788828
Proc Natl Acad Sci U S A. 1976 Oct;73(10):3333-7
1068445
Eur J Biochem. 1976 Dec;71(1):63-76
1009955
Anal Biochem. 1976 Dec;76(2):458-86
998986
Biochemistry. 1969 Dec;8(12):5149-60
5365801
J Am Chem Soc. 1973 Feb 21;95(4):1150-3
4687684
J Am Chem Soc. 1973 Feb 21;95(4):1154-9
4347146
Biochim Biophys Acta. 1975 Jun 12;392(2):319-27
165836
J Am Chem Soc. 1974 Jul 24;96(15):4815-9
4854397
J Am Chem Soc. 1974 Jul 10;96(14):4452-63
4854396
Biochem Biophys Res Commun. 1974 Apr 8;57(3):654-9
4827828
J Biol Chem. 1974 May 10;249(9):2959-73
4828331
J Biol Chem. 1974 Feb 10;249(3):682-90
4855813
Biochem Biophys Res Commun. 1974 Feb 4;56(3):555-60
4857053
J Am Chem Soc. 1973 Mar 21;95(6):2048-9
4689928
J Biol Chem. 1972 Jul 10;247(13):4219-23
5064341
J Am Chem Soc. 1972 Mar 8;94(5):1559-62
5015671
J Am Chem Soc. 1975 Nov 26;97(24):7185-6
1184895
J Am Chem Soc. 1975 Oct 1;97(20):5924-6
1159249
J Biol Chem. 1975 Mar 25;250(6):2363-9
1117008
J Am Chem Soc. 1975 Mar 19;97(6):1427-39
1133392
Biochem Biophys Res Commun. 1971 Apr 16;43(2):423-8
5577453
J Am Chem Soc. 1971 Apr 21;93(8):2035-40
5551904
J Biol Chem. 1966 Nov 25;241(22):5238-43
5928000
J Gen Physiol. 1965 Sep;49(1):Suppl:105-26
5859923