Kinetic studies of electron transfer in the cyt b
5 : metHb system

Qiao, Tiecheng; Witkowski, R.E.; Henderson, Robin Chandler; McLendon, George

doi:10.1007/s007750050075

Cited by 8 publications

(10 citation statements)

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“…Such a proposed binding site is consistent with the results of the variant study, in that Lys 16 (A14) of the α-chain is not involved with b 5 binding . Such a site would be influenced by the T−R conversion . A complementary β 1 β 2 -site situated near the IHP binding site could involve Lys residues at positions 8 (A5), 82 (EF6), and 144 (HC1) on the two β-chains as indicated in Figure C.…”

Section: Discussionsupporting

confidence: 85%

“…Given the agreement with Mauk and Mauk, we are unable to account for a report that the binding constant is more than an order of magnitude less …”

Section: Referencesmentioning

confidence: 86%

“…These studies showed that the binding of b 5 to Hb depends on both ionic strength and pH, indicating that electrostatic interactions stabilize this ET complex. In contrast, McLendon and co-workers recently suggested that prior complex formation may not be necessary for ET between these partners …”

Section: Introductionmentioning

confidence: 93%

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Binding and Electron Transfer between Cytochrome b₅ and the Hemoglobin α- and β-Subunits through the Use of [Zn, Fe] Hybrids

et al. 1998

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We have measured the binding affinity (K A ) and electron transfer (ET) rate constants (k) for the complex of hemoglobin (Hb) and cytochrome b 5 (b 5 ), using triplet quenching titrations of mixed-metal [ZnM, Fe 3+ (N 3 -)] Hb hybrids and of fully substituted Zn-mesoporphyrin (ZnM)Hb by b 5 (trypsin-solubilized, bovine) (pH values 6.0 and 7.0). The use of the mixed-metal Hb hybrids with Zn in one chain type allows us to selectively monitor the 3 ZnP f Fe 3+ P ET reaction of Fe 3+ b 5 with either the R-chains or the β-chains. The self-consistent analysis of the results for the mixed-metal hybrids and those for the (ZnM)Hb allows us to determine the reactivity and affinity constants for the interactions of b 5 with the individual subunits of T-state Hb. The results confirm that ET occurs within a complex between b 5 and Hb, not through a simple bimolecular collision process. At pH 6.0, the binding affinity constant of the R-chains (K R ≈ 2.0 × 10 4 M -1 ) is ∼4-fold larger than that of the β-chains (K β ) 4.9 × 10 3 M -1 ); the intracomplex ET rate constant of the R-chains (k R ≈ 1500 s -1 ) is ∼2-fold larger than that of the β-chains (k β ≈ 850 s -1 ). The binding affinity and ET rate constant of the R-chains both decrease as the pH is increased from 6.0 to 7.0; the binding affinity of the β-chains is essentially the same at pH 6.0 and 7.0, while the ET reactivity decreases. The kinetic results are consistent with a docking model in which each subunit binds a molecule of b 5 . However, they permit an alternative in which b 5 reacts with the R-chains by binding at a site which spans the R 1 β 2 dimer interface.

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Section: Discussionsupporting

confidence: 85%

“…Given the agreement with Mauk and Mauk, we are unable to account for a report that the binding constant is more than an order of magnitude less …”

Section: Referencesmentioning

confidence: 86%

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Binding and Electron Transfer between Cytochrome b₅ and the Hemoglobin α- and β-Subunits through the Use of [Zn, Fe] Hybrids

et al. 1998

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“…As the concentration of diMePH 4 was increased, the rate constant of the rapid initial phase increased (inset to Figure 2, k + = 9.5 M −1 • s −1 ) and the magnitude of the absorbance change remained constant and corresponded to the rapid reduction of one subunit out of four in metHb. The observation of biphasic kinetics was in agreement with the previously reported kinetic data on the reduction of metHb by ferrocyt b 5 [30], which indicated that the second and subsequent subunits may react at a rate different from that of the first one.…”

Section: Figure 1 Reduction Of Cyt C By Dimephsupporting

confidence: 92%

Reduction of ferric haemoproteins by tetrahydropterins: a kinetic study

Capeillère‐Blandin

Mathieu

Mansuy

2005

Biochemical Journal

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We previously showed that one-electron transfer from tetrahydropterins to iron porphyrins is a very general reaction, with formation of an intermediate cation radical similar to the one detected in NO synthase. As a model reaction, the rates of reduction of eight haemoproteins by diMePH4 (6,7-dimethyltetrahydropterin) have been studied and correlated with their one-electron reduction potentials, E(m) (Fe(III)/Fe(II)). On the basis of kinetic data analyses, a bimolecular collisional mechanism is proposed for the electron transfer from diMePH4 to ferrihaemoproteins. Haemoproteins with reduction potentials below -160 mV were shown not to be reduced by diMePH4 to the corresponding ferrohaemoproteins. For haemoproteins with reduction potentials more positive than -160 mV, such as chloroperoxidase, cytochrome b5, methaemoglobin and cytochrome c, there was a good correlation between the second-order reduction rate constant and the redox potential, E(m) (Fe(III)/Fe(II)): [formula: see text]. The rate of reduction of cytochrome c by BH4 [(6R)-5,6,7,8-tetrahydrobiopterin] was determined to be similar to that of the reduction of cytochrome c by diMePH4. These results confirm the role of tetrahydropterins as one-electron donors to Fe(III) porphyrins.

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“…The study of the interaction between cytochrome b 5 and hemoglobin is important because it allows the possibility to investigate biological electron transfer between physiological partners. , Because of its physiological importance, the system has been largely investigated by different groups. ,− In particular, electron-transfer rates were determined using heme proteins reconstituted with photoactive heme groups. , The kinetics of met-hemoglobin reduction by cytochrome b 5 have also been studied by saturation transfer NMR and stopped-flow NMR …”

Section: 9 Cytochrome B 5/hemoglobin (Myoglobin)mentioning

confidence: 99%

Mechanism of Electron Transfer in Heme Proteins and Models: The NMR Approach

Simonneaux

Bondon

2005

Chem. Rev.

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Kinetic studies of electron transfer in the cyt b 5 : metHb system

Cited by 8 publications

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Binding and Electron Transfer between Cytochrome b₅ and the Hemoglobin α- and β-Subunits through the Use of [Zn, Fe] Hybrids

Binding and Electron Transfer between Cytochrome b₅ and the Hemoglobin α- and β-Subunits through the Use of [Zn, Fe] Hybrids

Reduction of ferric haemoproteins by tetrahydropterins: a kinetic study

Mechanism of Electron Transfer in Heme Proteins and Models: The NMR Approach

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Kinetic studies of electron transfer in the cyt b 5 : metHb system

Cited by 8 publications

References 0 publications

Binding and Electron Transfer between Cytochrome b5 and the Hemoglobin α- and β-Subunits through the Use of [Zn, Fe] Hybrids

Binding and Electron Transfer between Cytochrome b5 and the Hemoglobin α- and β-Subunits through the Use of [Zn, Fe] Hybrids

Reduction of ferric haemoproteins by tetrahydropterins: a kinetic study

Mechanism of Electron Transfer in Heme Proteins and Models: The NMR Approach

Contact Info

Product

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Binding and Electron Transfer between Cytochrome b₅ and the Hemoglobin α- and β-Subunits through the Use of [Zn, Fe] Hybrids

Binding and Electron Transfer between Cytochrome b₅ and the Hemoglobin α- and β-Subunits through the Use of [Zn, Fe] Hybrids