Viscosity-dependent relaxation significantly modulates the kinetics of CO recombination in the truncated hemoglobin TrHbN from Mycobacterium tuberculosis.

The Journal of Biological Chemistry
David DantskerJoel M Friedman

Abstract

Kinetic traces were generated for the nanosecond and slower rebinding of photodissociated CO to trHbN in solution and in porous sol-gel matrices as a function of viscosity, conformation, and mutation. TrHbN is one of the two truncated hemoglobins from Mycobacterium tuberculosis. The kinetic traces were analyzed in terms of three distinct phases. These three phases are ascribed to rebinding: (i) from the distal heme pocket, (ii) from the adjacent apolar tunnel prior to conformational relaxation, and (iii) from the apolar tunnel subsequent to conformational relaxation. The fractional content of each of these phases was shown to be a function of the viscosity and, in the case of the sol-gel-encapsulated samples, sample preparation history. The observed kinetic patterns support a model consisting of the following elements: (i) the viscosity and conformation-sensitive dynamics of the Tyr(B10) side chain facilitate diffusion of the dissociated ligand from the distal heme pocket into the adjacent tunnel; (ii) the distal heme pocket architecture determines ligand access from the tunnel back to the heme iron; (iii) the distal heme pocket architecture is governed by a ligand-dependent hydrogen bonding network that limits the range of acc...Continue Reading

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Citations

Jun 5, 2013·Physical Chemistry Chemical Physics : PCCP·Stefania AbbruzzettiCristiano Viappiani
Mar 25, 2008·The Journal of Biological Chemistry·Raymond M EsquerraRobert A Goldbeck
Oct 4, 2007·Journal of the American Chemical Society·Uri SamuniJoel M Friedman

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