Oxygen binding and oxidation reactions of human hemoglobin conjugated to carboxylate dextran.
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.
Jia
Yiping
Y
Laboratory of Biochemistry and Vascular Biology, Center for Biologics Evaluation and Research, Food and Drug Administration, Bethesda, MD 20892, USA.
Wood
Francine
F
Menu
Patrick
P
Faivre
Béatrice
B
Caron
Alexis
A
Alayash
Abdu I
AI
D003911:Dextrans / Q000737:chemistry* / Q000378:metabolism*; D006418:Heme / Q000737:chemistry / Q000378:metabolism; D006454:Hemoglobins / Q000737:chemistry* / Q000378:metabolism*; D006801:Humans; D006861:Hydrogen Peroxide / Q000494:pharmacology; D006863:Hydrogen-Ion Concentration; D007700:Kinetics; D008024:Ligands; D010084:Oxidation-Reduction / Q000187:drug effects; D010100:Oxygen / Q000378:metabolism*; D010833:Phytic Acid / Q000494:pharmacology; D013050:Spectrometry, Fluorescence; D013053:Spectrophotometry; D013816:Thermodynamics
D003911:Dextrans; D006454:Hemoglobins; D008024:Ligands; D006418:Heme; D010833:Phytic Acid; D006861:Hydrogen Peroxide; D010100:Oxygen