RAAP, Adriaan;
van LEEUWEN, Johan W.;
van ECK‐SCHOUTEN, Tony;
ROLLEMA, Harry S.;
de BRUIN, Simon H.
Heterogeneity in the Kinetics of Oxygen Binding to Partially Reduced Human Methemoglobin : A Pulse‐Radiolysis Study of Oxygenated Solutions of Methemoglobin
: A Pulse‐Radiolysis Study of Oxygenated Solutions of Methemoglobin
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Medientyp:
E-Artikel
Titel:
Heterogeneity in the Kinetics of Oxygen Binding to Partially Reduced Human Methemoglobin : A Pulse‐Radiolysis Study of Oxygenated Solutions of Methemoglobin
:
A Pulse‐Radiolysis Study of Oxygenated Solutions of Methemoglobin
Beteiligte:
RAAP, Adriaan;
van LEEUWEN, Johan W.;
van ECK‐SCHOUTEN, Tony;
ROLLEMA, Harry S.;
de BRUIN, Simon H.
Beschreibung:
<jats:p>The pulse‐radiolysis technique has been introduced because it permits a rapid reduction (in a few microseconds) of one heme group of the methemoglobin tetramer by hydrated electrons. The kinetics of the binding of oxygen to this particular valence intermediate (Hb<jats:sup>3+</jats:sup>) with one reduced α or β subunit has been studied. It appears that the hydrated electrons preferentially reduce one type of subunit of methemoglobin at acid and neutral pH‐values as is shown by the biphasic behaviour of Hb<jats:sup>3+</jats:sup> on oxygenation. The second‐order on‐rate constants measured for the binding of oxygen to Hb<jats:sup>3+</jats:sup> are 14 ± 3 mM<jats:sup>−1</jats:sup> ms<jats:sup>−1</jats:sup> and 56 ± 9 mM<jats:sup>−1</jats:sup> ms<jats:sup>−1</jats:sup>, respectively. The relative contribution of the faster fraction is about 0.63 ± 0.08 of the total oxygenation process.</jats:p><jats:p>A comparison of the kinetic absorbance difference spectrum for the reduction of methemoglobin with the static difference spectrum of deoxyhemoglobin and methemoglobin in the Soret‐region revealed a decreased absorbance of the unliganded subunit of Hb<jats:sup>3+</jats:sup> at 430 nm. This fact suggests that Hb<jats:sup>3+</jats:sup> is in the relaxed quaternary conformation, which is in agreement with the observed on‐rate constants.</jats:p>