Haptoglobin alters oxygenation and oxidation of hemoglobin and decreases propagation of peroxide-induced oxidative reactions.

Journal Article (Journal Article)

We compared oxygenation and anaerobic oxidation reactions of a purified complex of human hemoglobin (Hb) and haptoglobin (Hb-Hp) to those of uncomplexed Hb. Under equilibrium conditions, Hb-Hp exhibited active-site heterogeneity and noncooperative, high-affinity O(2) binding (n(1/2)=0.88, P(1/2)=0.33 mm Hg in inorganic phosphate buffer at pH 7 and 25 °C). Rapid-reaction kinetics also exhibited active-site heterogeneity, with a slower process of O(2) dissociation and a faster process of CO binding relative to uncomplexed Hb. Deoxygenated Hb-Hp had significantly reduced absorption at the λ(max) of 430 nm relative to uncomplexed Hb, as occurs for isolated Hb subunits that lack T-state stabilization. Under comparable experimental conditions, the redox potential (E(1/2)) of Hb-Hp was found to be +54 mV, showing that it is much more easily oxidized than uncomplexed Hb (E(1/2)=+125 mV). The Nernst plots for Hb-Hp oxidation showed no cooperativity and slopes less than unity indicated active-site heterogeneity. The redox potential of Hb-Hp was unchanged by pH over the range of 6.4-8.3. Exposure of Hb-Hp to excess hydrogen peroxide (H(2)O(2)) produced ferryl heme, which was found to be more kinetically inert in the Hb-Hp complex than in uncomplexed Hb. The negative shift in the redox potential of Hb-Hp and its stabilized ferryl state may be central elements in the protection against Hb-induced oxidative damage afforded by formation of the Hb-Hp complex.

Full Text

Duke Authors

Cited Authors

  • Banerjee, S; Jia, Y; Siburt, CJP; Abraham, B; Wood, F; Bonaventura, C; Henkens, R; Crumbliss, AL; Alayash, AI

Published Date

  • September 2012

Published In

Volume / Issue

  • 53 / 6

Start / End Page

  • 1317 - 1326

PubMed ID

  • 22841869

Electronic International Standard Serial Number (EISSN)

  • 1873-4596

International Standard Serial Number (ISSN)

  • 0891-5849

Digital Object Identifier (DOI)

  • 10.1016/j.freeradbiomed.2012.07.023


  • eng