User:Adam Mirando/Sandbox 1: Difference between revisions

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===Redox Potential===

The redox potential of bovine XOR differs between the XO and XDH forms and may partly explain the difference in specificity for their final electron acceptors. Microcoulometry measurements of the mid-point potentials for the cofactors of XO at pH 7.7, 25 °C were as follows: MoVI/MoV, -375 mV; Mov/MoIV, -405 mV; Fe-S Iox/red, -320 mV; Fe-S IIox/red, -230 mV; FAD/FADH2, -280 mV <ref>PMID:6282314</ref>. The Em of xanthine/urate at pH 7.65 was -410 mV, indicating that the oxidation of xanthine by the enzyme is favored and that the electron affinity of the enzyme cofactors approximately follows FAD ≥ Fe/S > Mo <ref name="thermo">PMID:11229448</ref>. In the case of XDH, the iron sulfur potentials appear similar to those of XO, - 310 and -234 mV for Fe-S I and Fe-S II respectively. However, the midpoint two electron reduction potential of FAD/FADH2 is -340 mV. Considering that the Em of NAD is -335 mV, the flavin midpoint potential of XDH appears suitable for the reduction of NAD+ to NADH while the corresponding potential FAD in XO (-280 mV) is too large <ref name="thermo" />. A possible explanation for this shift in mid-point potential could be the exchange of interactions accompanying the conversion of XDH to XO. In XDH Asp429 is in direct interaction with the flavin coenzyme. However, the cleavage- or oxidation-induced shift of residues 422-432 exchanges Asp429 for Arg426, thereby modifying the electrostatic potential of FAD<ref name="structure" />.

The redox potential of bovine XOR differs between the XO and XDH forms and may partly explain the difference in specificity for their final electron acceptors. Microcoulometry measurements of the mid-point potentials for the cofactors of XO at pH 7.7, 25 °C were as follows: MoVI/MoV, -375 mV; Mov/MoIV, -405 mV; Fe-S Iox/red, -320 mV; Fe-S IIox/red, -230 mV; FAD/FADH2, -280 mV <ref>PMID:6282314</ref>. The Em of xanthine/urate at pH 7.65 was -410 mV, indicating that the oxidation of xanthine by the enzyme is favored and that the electron affinity of the enzyme cofactors approximately follows FAD ≥ Fe/S > Mo <ref name="thermo">PMID:11229448</ref>. In the case of XDH, the iron sulfur potentials appear similar to those of XO, - 310 and -234 mV for Fe-S I and Fe-S II respectively. However, the midpoint two electron reduction potential of FAD/FADH2 is -340 mV. The binding of NAD+ to the FAD domain increases this midpoint potential, facilitating the transfer of electrons from the iron-sulfur centers to FAD. Considering that the Em of NAD is -335 mV, the flavin midpoint potential of XDH appears suitable for the reduction of NAD+ to NADH while the corresponding potential FAD in XO (-280 mV) is too large <ref name="thermo" />. A possible explanation for this shift in mid-point potential could be the exchange of interactions accompanying the conversion of XDH to XO. In XDH Asp429 is in direct interaction with the flavin coenzyme. However, the cleavage- or oxidation-induced shift of residues 422-432 exchanges Asp429 for Arg426, thereby modifying the electrostatic potential of FAD<ref name="structure" />.

== References ==

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 ===Redox Potential===
-The redox potential of bovine XOR differs between the XO and XDH forms and may partly explain the difference in specificity for their final electron acceptors. Microcoulometry measurements of the mid-point potentials for the cofactors of XO at pH 7.7, 25 °C were as follows: MoVI/MoV, -375 mV; Mov/MoIV, -405 mV; Fe-S I<sub>ox/red</sub>, -320 mV; Fe-S II<sub>ox/red</sub>, -230 mV; FAD/FADH<sub>2</sub>, -280 mV <ref>PMID:6282314</ref>.  The E<sub>m</sub> of xanthine/urate at pH 7.65 was -410 mV, indicating that the oxidation of xanthine by the enzyme is favored and that the electron affinity of the enzyme cofactors approximately follows FAD ≥ Fe/S > Mo <ref name="thermo">PMID:11229448</ref>. In the case of XDH, the iron sulfur potentials appear similar to those of XO, - 310 and -234 mV for Fe-S I and Fe-S II respectively. However, the midpoint two electron reduction potential of FAD/FADH<sub>2</sub> is -340 mV. Considering that the E<sub>m</sub> of NAD is -335 mV, the flavin midpoint potential of XDH appears suitable for the reduction of NAD<sup>+</sup> to NADH while the corresponding potential FAD in XO (-280 mV) is too large <ref name="thermo" />. A possible explanation for this shift in mid-point potential could be the exchange of interactions accompanying the conversion of XDH to XO. In XDH Asp429 is in direct interaction with the flavin coenzyme. However, the cleavage- or oxidation-induced shift of residues 422-432 exchanges Asp429 for Arg426, thereby modifying the electrostatic potential of FAD<ref name="structure" />.
+The redox potential of bovine XOR differs between the XO and XDH forms and may partly explain the difference in specificity for their final electron acceptors. Microcoulometry measurements of the mid-point potentials for the cofactors of XO at pH 7.7, 25 °C were as follows: MoVI/MoV, -375 mV; Mov/MoIV, -405 mV; Fe-S I<sub>ox/red</sub>, -320 mV; Fe-S II<sub>ox/red</sub>, -230 mV; FAD/FADH<sub>2</sub>, -280 mV <ref>PMID:6282314</ref>.  The E<sub>m</sub> of xanthine/urate at pH 7.65 was -410 mV, indicating that the oxidation of xanthine by the enzyme is favored and that the electron affinity of the enzyme cofactors approximately follows FAD ≥ Fe/S > Mo <ref name="thermo">PMID:11229448</ref>. In the case of XDH, the iron sulfur potentials appear similar to those of XO, - 310 and -234 mV for Fe-S I and Fe-S II respectively. However, the midpoint two electron reduction potential of FAD/FADH<sub>2</sub> is -340 mV. The binding of NAD<sup>+</sup> to the FAD domain increases this midpoint potential, facilitating the transfer of electrons from the iron-sulfur centers to FAD. Considering that the E<sub>m</sub> of NAD is -335 mV, the flavin midpoint potential of XDH appears suitable for the reduction of NAD<sup>+</sup> to NADH while the corresponding potential FAD in XO (-280 mV) is too large <ref name="thermo" />. A possible explanation for this shift in mid-point potential could be the exchange of interactions accompanying the conversion of XDH to XO. In XDH Asp429 is in direct interaction with the flavin coenzyme. However, the cleavage- or oxidation-induced shift of residues 422-432 exchanges Asp429 for Arg426, thereby modifying the electrostatic potential of FAD<ref name="structure" />.
 == References ==
 <references/>