Title

Heme orientational disorder in reconstituted and native sperm whale myoglobin. Proton nuclear magnetic resonance characterizations by heme methyl deuterium labeling in the met-cyano protein

Document Type

Article

Publication Date

8-25-1983

Abstract

The solution proton nuclear magnetic resonance spectrum of the Met-cyano form of sperm whale myoglobin reveals the presence of two sets of comparably intense resonances immediately after reacting the apoprotein with hemin, only one of which corresponds to that of the accepted native protein. Isotope labeling of individual methyl groups of hemin reveals that the methyl assignments differ characteristically in that similar resonance positions for the two components arise from the methyl groups related by a 180° rotation about the α-γ-meso axis. This phenomenon, observed earlier only for myoglobin with modified hemin, dictates that the second protein component in solution immediately after reconstitution must have the heme rotated by 180° about the α-γ-meso axis as compared to that found in the single crystal. The two components in the reconstituted protein equilibrate to yield the spectrum of the native Met-cyanomyoglobin for which there still exists approximately 8% of the minor component. Thus native myoglobin in solution is structurally heterogeneous in the heme pocket. Proton nuclear magnetic resonance spectra of deoxymyoglobin produced from both native and freshly reconstituted protein shown that the heterogeneity is also a property of the physiologically relevant reduced protein forms. It is suggested that, contrary to available X-ray data, heme orientational heterogeneity may be the rule rather than the exception in b-type hemoproteins, and that such disorder must be carefully considered in detailed correlations between structure and function even in native hemoproteins. © 1983 Academic Press Inc. (London) Ltd.

Publication Source (Journal or Book title)

Journal of Molecular Biology

First Page

887

Last Page

896

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