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Published March 1983 | public
Journal Article

Mechanism of T_1 relaxation in ^(13)CO complexed to an iron porphyrin: implications for CO bonding in heme proteins

Abstract

Chemical shifts and spin-lattice relaxation parameters for ^(13)CO bonded to the complex 1 -methylimidazole-iron protoporphyrin dimethyl ester are reported. The ^(13)CO chemical shifts are much different from those observed in the carbonyl vertebrate hemoglobins, but remarkably similar to that observed for the monomeric hemoglobin component from Glycera dibranchiata. The relaxation parameter, T_1, is shown to change dramatically upon ligation to both the hemin model system and to hemoglobin A. The mechanisms of spin-lattice relaxation are dominated by chemical shift anisotropy for ^(13)CO bound to both hemins and proteins, but, in the latter, dipole-dipole forces make an additional contribution to the overall relaxation rate.

Additional Information

© 1983 American Chemical Society. Received June 10, 1982. Contribution No. 6753 from the Departments of Chemistry, California Institute of Technology, Pasadena, California 91125, and the University of New Mexico. Albuquerque, New Mexico 87131. This work was supported by National Institutes of Health Grants GM 16424, HL 15162, and HL 13581. The HSX-360 Regional Facility (Stanford Magnetic Resonance Laboratory) was supported by National Institutes of Health Grant RR-00711 and National Science Foundation Grant GR-23633. J.D.S. also wishes to acknowledge support from Sandia Corp. during the preparation of this manuscript. Further, we gratefully acknowledge the cooperation of Professor J. D. Roberts and the use of his Bruker WH-180 spectrometer (supported by GM-11072). One of us (T.G.P.) thanks John G. Reynolds (S.M.R.L.) for help in obtaining the 8.45-T spectra and Dr. James Sudmeier (U.C. Riverside) for many helpful discussions.

Additional details

Created:
August 19, 2023
Modified:
October 23, 2023