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The reversible reduction of horse metmyoglobin by the iron(II) complex of trans-1,2-diaminocyclohexane-N,N,N,n-tetraacetate.
Metadata
Journalbiochemistry2.865Date
1975-Dec-16
Publication Type
Research Support, U.S. Gov't, Non-P.H.S.
Journal Article
Volume
1975-Dec-16 / 14 : 5470-5
Author
Cassatt JC , Marini CP , Bender JW
DoiPMIDMESH
Acetates
Animals
Chelating Agents
Cyanides
Cyclohexylamines
Edetic Acid
Ferrous Compounds
Horses
Hydrogen-Ion Concentration
Iron
Kinetics
Myoglobin
Nitric Oxide
Oxidation-Reduction
Oxygen
Protein Binding
Abstract
The reduction of metmyoglobin by the iron(II) complex of trans-1,2-diaminocyclohexane-N,N,N'N'-tetraacetate (FeCDTA2-) has been investigated. The equilibrium constant, measured spectrophotometrically, is 0.21 with a resulting reduction potential of 0.050 V for Mb0. The rate constant for the reduction is 28 M-1 sec-1 with a deltaH ++ of 13 kcal M-1 and deltaS ++ of -11 eu. Both CN- and OH- inhibit the reduction because of the relatively low reactivity of cyanometmyoglobin (Mb+CN-) and ionized metmyglobin (Mb+OH-). The rate constant for the reduction of Mb+CN- by FeCDTA2- is 4.0 X 10(-2) M-1 sec-1 and that for reduction of Mb+OH- is 4.8 M-1 sec-1. The nitric oxide complex of metmyoglobin is reduced with a rate constant of 10 M-1 sec-1. The kinetics of oxidation of oxymyoglobin by FeCDTA- were studied. The data are consistent with a mechanism where oxidation takes place entirely through the deoxy form. A rate constant of 1.45 X 10(2) M-1 sec-1 was calculated for the oxidation of deoxymyoglobin by FeCDTA-, in equilibrium constant and rate constant for reduction. The above data are discussed in terms of a simple outer-sphere reduction reaction.
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Biochemistrybiochemistry
Metadata
LocationUnited States
FromAMER CHEMICAL SOC

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