Extreme differences between hemoglobins I and II of the clam Lucina pectinalis in their reactions with nitrite.

Journal Article

The clam Lucina pectinalis supports its symbiotic bacteria by H₂S transport in the open and accessible heme pocket of Lucina Hb I and by O₂ transport in the narrow and crowded heme pocket of Lucina Hb II. Remarkably, air-equilibrated samples of Lucina Hb I were found to be more rapidly oxidized by nitrite than any previously studied Hb, while those of Lucina Hb II showed an unprecedented resistance to oxidation induced by nitrite. Nitrite-induced oxidation of Lucina Hb II was enabled only when O₂ was removed from its active site. Structural analysis revealed that O₂ "clams up" the active site by hydrogen bond formation to B10Tyr and other distal-side residues. Quaternary effects further restrict nitrite entry into the active site and stabilize the hydrogen-bonding network in oxygenated Lucina Hb II dimers. The dramatic differences in nitrite reactivities of the Lucina Hbs are not related to their O₂ affinities or anaerobic redox potentials, which were found to be similar, but are instead a result of differences in accessibility of nitrite to their active sites; i.e. these differences are due to a kinetic rather than thermodynamic effect. Comparative studies revealed heme accessibility to be a factor in human Hb oxidation by nitrite as well, as evidenced by variations of rates of nitrite-induced oxidation that do not correlate with R and T state differences and inhibition of oxidation rate in the presence of O₂. These results provide a dramatic illustration of how evolution of active sites with varied heme accessibility can moderate the rates of inner-sphere oxidative reactions of Hb and other heme proteins.

Full Text

Duke Authors

Cited Authors

  • Bonaventura, C; Henkens, R; De Jesus-Bonilla, W; Lopez-Garriga, J; Jia, Y; Alayash, AI; Siburt, CJP; Crumbliss, AL

Published Date

  • October 2010

Published In

Volume / Issue

  • 1804 / 10

Start / End Page

  • 1988 - 1995

PubMed ID

  • 20601225

International Standard Serial Number (ISSN)

  • 0006-3002

Digital Object Identifier (DOI)

  • 10.1016/j.bbapap.2010.06.016

Language

  • eng

Conference Location

  • Netherlands