Scientific Publications by FDA Staff

Biochim Biophys Acta 2004 Jun 11;1672(3):164-73

Oxygen binding and oxidation reactions of human hemoglobin conjugated to carboxylate dextran.

Jia Y, Wood F, Menu P, Faivre B, Caron A, Alayash AI

Alayash AI, US FDA, Ctr Biol Evaluat & Res, Lab Biochem & Vasc Biol, 8800 Rockville Pike,NIH Bldg,29,Room 112, Bethesda, MD 20892 USA US FDA, Ctr Biol Evaluat & Res, Lab Biochem & Vasc Biol, Bethesda, MD 20892 USA Univ Henri Poincare Nancy, Sch Pharm, Dept Hematol & Physiol, F-54001 Nancy, France

Human hemoglobin (Hb) conjugated to benzene tetracarboxylate substituted dextran produces a polymeric Hb (Dex-BTC-Hb) with similar oxygen affinity to that of red blood cells (P(50)=28-29 mm Hg). Under physiological conditions, the oxygen affinity (P(50)) of Dex-BTC-Hb is 26 mm Hg, while that of native purified human HbA(0) is 14 mm Hg, but it exhibits a slight reduction in cooperativity (n(50)), Bohr effect, and lacks sensitivity to inositol hexaphosphate (IHP), when compared to HbA(0). Oxygen-binding kinetics, measured by rapid mixing stopped-flow method showed comparable oxygen dissociation and association rates for both HbA(0) and Dex-BTC-Hb. The rate constant for NO-mediated oxidation of the oxy form of Dex-BTC-Hb, which is governed by NO entry to the heme pocket, was reduced to half of the value obtained for HbA(0). Moreover, Dex-BTC-Hb is only slightly more sensitive to oxidative reactions than HbA(0), as shown by about 2-fold increase in autoxidation, and slightly higher H(2)O(2) reaction and heme degradation rates. Dextran-BTC-based modification of Hb produced an oxygen-carrying compound with increased oxygen release rates, decreased oxygen affinity and reduced nitric oxide scavenging, desirable properties for a viable blood substitute. However, the reduction in the allosteric function of this protein and the lack of apparent quaternary T-->R transition may hinder its physiological role as an oxygen transporter.