VIBRATIONAL CIRCULAR DICHROISM STUDIES OF AZIDOMETHEMOGLOBIN AND AZIDOMETYOGLOBIN

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We have investigated the vibrational circular dichroism associated with the antisymmetric stretch of azide ion bound to several methemoglobins (human, carp) and metmyoglobins (horse, sperm whale, reconstituted with modified heme, and mutant). There is no VCD intensity correspondin to the absorption feature arising from azide bound to high-spin iron. A negative VCD feature $(g = -1.3 \times 10^{3})$ is observed for azide ion bound to low-spin iron; this feature is absent in a mutant myolobin in which the distal histidine is replaced with glycine. For the normal proteins, the VCD anistropy ratio is slightly larger in myoglobin compared to hemoglobin, but is not affected by using $D_{2}O$ rather than $H_{2}O$ solvent. Our results differ in magnitude from those originally reported by Marcott $et al^{1}$. The relationship between the structure of the ligand binding site in the heme proteins and the VCD intensity wil be discussed

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$^{1}$ Marcott, C: Havel, H.A: Hedland, F; Overend, J.; Moscowitz, A. In Optical Activity and Chiral Discrimination, Mason, S. F.. Ed., Reidel, Dordrecht, 1979, pp 289.292.
Author Institution: Department of Chemistry, Syracuse University; Department of Chemistry, University of Pittsburgh; Department of Biochemistry, University of lllinois; Department of Medicine and Biochemistry, State University of New York

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