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The Effect of Heme-linked Ionizable Groups on Cyanide Binding to Methemoglobin*

Vega-Catalan, F. J. and Odeyemi, O. J. and Okonjo, K. O. (1986) The Effect of Heme-linked Ionizable Groups on Cyanide Binding to Methemoglobin*. The Journal of Biological Chemistry, 261 (23). pp. 10576-10578.

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The pH dependence of the kinetics of the binding of cyanide ion to methemoglobins A and S and to guinea pig and pigeon methemoglobins appears to be not directly correlated with the net charges on the proteins. The kinetics can, howeverb, e adequately explained in terms of three sets of heme-linked ionizable groups with pK, ranging between 4.9 and 5.3, pK, between 6.2 and 7.9, and pK3 between 8.0 and 8.5 at 20 “C. pK1 is assigned to carboxylic acid groups, pKZ to histidines and terminal amino groups, and pK3 to the acidalkaline methemoglobin transition. Kinetic second order rate constants have also been determined for the binding of cyanide ion by the four sets of methemoglobin species present in solution. The pKi values and the rate constants of methemoglobin S are strikingly different from those of methemoglobin A. This result is explained in terms of different electrostatic contributions to the free energy of heme linkage arising from differences in the environments of ionizable groups at the surfaces of the two molecules.

Item Type: Article
Subjects: Q Science > QD Chemistry
Divisions: Faculty of Engineering, Science and Mathematics > School of Chemistry
Depositing User: Mr Adewole Adewumi
Date Deposited: 02 Jul 2011 10:44
Last Modified: 13 Dec 2011 21:13

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