De-Jia LI, Hua LUO,
Li-Ling WANG, and Guo-Lin ZOU*
( College of Life Sciences, Wuhan University, Wuhan 430072, China )
Abstract Superoxide
anion and NO can react to form the highly oxidizing species peroxynitrite (ONOO–)
which can react directly with hemoglobin (Hb) even in the presence of physiological
concentration CO2. This research was to determine the ONOO–mediated
oxidation damage to the heme of oxyhemoglobin (oxyHb) under conditions expected
in blood. Results showed that 8-10 mol ONOO– was needed to quickly
and completely convert 1 mol oxyHb to methemoglobin (metHb). ONOO–
(20-140 米M) caused rapid and extensive formation of metHb from oxyHb (50 米M)
mainly occurring within first 5-20 min of incubation. The conversion efficiency
reached 16%, 48%, 60%, 79% and 88% output of metHb after 90 min of incubation
at 0, 20, 40, 100, and 140 米M ONOO– respectively. 1 mM CO2
caused a small decrease in the ability of ONOO– to oxidize oxyHb,
and ONOO–-promoted conversion of oxyHb to metHb increased when pH
decreased from 8.0 to 6.0. Relatively lower temperature in blood condition will
inhibit this reaction in some degree. We postulate that ONOO– can
mediate oxidation damage to the heme, and cause heme loss from the hydrophobic
cavity of Hb when its concentration exceeded 90 米M. These results indicated
that ONOO– could convert oxyHb to metHb under the conditions expected
in blood, and this reaction was regulated by CO2 concentration, reaction
time, temperature and pH value.
Key words hemoglobin;
peroxynitrite; heme; methemoglobin
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Received:
September 22, 2003 Accepted: December 2, 2003
This work was supported by a grant from the National Natural Science Foundation
of China (No. 39770200)
*Corresponding author: Tel, 86-27-87645674; Fax, 86-27-87669560; E-mail, [email protected]