Identification of the titrating group in the heme cavity of myoglobin
The pH dependence of the proton NMR chemical shifts of met‐cyano and deoxy forms of native and reconstituted myoglobins reflects a structural transition in the heme pocket modulated by a single proton with p K 5.1–5.6. Comparison of this pH dependence of sperm whale and elephant myoglobin and that o...
| Published in: | European Journal of Biochemistry |
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| Main Authors: | , |
| Format: | Article in Journal/Newspaper |
| Language: | English |
| Published: |
Wiley
1984
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| Subjects: | |
| Online Access: | http://dx.doi.org/10.1111/j.1432-1033.1984.tb07892.x https://api.wiley.com/onlinelibrary/tdm/v1/articles/10.1111%2Fj.1432-1033.1984.tb07892.x https://febs.onlinelibrary.wiley.com/doi/pdf/10.1111/j.1432-1033.1984.tb07892.x |
| Summary: | The pH dependence of the proton NMR chemical shifts of met‐cyano and deoxy forms of native and reconstituted myoglobins reflects a structural transition in the heme pocket modulated by a single proton with p K 5.1–5.6. Comparison of this pH dependence of sperm whale and elephant myoglobin and that of the former protein reconstituted with esterified hemin eliminates both the distal histidine as well as the heme propionates as the titrating residue. Reconstitution of sperm whale met‐cyano myoglobin with hemin modified at the 2,4‐positions leads to a systematic variation in the p K for the structural transition, thus indicating the presence of a coupling between the titrating group and the heme π system. The results are consistent with histidine FG3 (His‐FG3) being the titrating group, and a donor‐acceptor π‐π interaction between its imidazole and the heme is proposed. |
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