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U.S. Department of Health and Human Services

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Nitric Oxide 2012 Jun 30;27(1):32-9

Enhanced nitrite reductase activity associated with the haptoglobin complexed hemoglobin dimer: Functional and antioxidative implications.

Roche CJ, Dantsker D, Alayash AI, Friedman JM


The presence of acellular hemoglobin (Hb) within the circulation is generally viewed as a pathological state that can result in toxic consequences. Haptoglobin (Hp), a globular protein found in the plasma, binds with high avidity the alphabeta dimers derived from the dissociation of Hb tetramer and thus helps clear free Hb. More recently there have been compelling indications that the redox properties of the Hp bound dimer (Hb-Hp) may play a more active role in controlling toxicity by limiting the potential tissue damage caused by propagation of the free-radicals generated within the heme containing globin chains. The present study further examines the potential protective effect of Hp through its impact on the production of nitric oxide (NO) from nitrite through nitrite reductase activity of the Hp bound alphabeta Hb dimer. The presented results show that the Hb dimer in the Hb-Hp complex has oxygen binding, CO recombination and spectroscopic properties consistent with an Hb species having properties similar to but not exactly the same as the R quaternary state of the Hb tetramer. Consistent with these observations is the finding that the initial nitrite reductase rate for Hb-Hp is approximately ten times that of HbA under the same conditions. These results in conjunction with the earlier redox properties of the Hb-Hp are discussed in terms of limiting the pathophysiological consequences of acellular Hb in the circulation.

Category: Journal Article
PubMed ID: #22521791 DOI: 10.1016/j.niox.2012.04.002
Includes FDA Authors from Scientific Area(s): Biologics
Entry Created: 2012-06-22 Entry Last Modified: 2012-08-29