12 research outputs found
Role of the Subunits Interactions in the Conformational Transitions in Adult Human Hemoglobin: an Explicit Solvent Molecular Dynamics Study
Hemoglobin exhibits allosteric structural changes upon ligand binding due to
the dynamic interactions between the ligand binding sites, the amino acids
residues and some other solutes present under physiological conditions. In the
present study, the dynamical and quaternary structural changes occurring in two
unligated (deoxy-) T structures, and two fully ligated (oxy-) R, R2 structures
of adult human hemoglobin were investigated with molecular dynamics. It is
shown that, in the sub-microsecond time scale, there is no marked difference in
the global dynamics of the amino acids residues in both the oxy- and the deoxy-
forms of the individual structures. In addition, the R, R2 are relatively
stable and do not present quaternary conformational changes within the time
scale of our simulations while the T structure is dynamically more flexible and
exhibited the T\rightarrow R quaternary conformational transition, which is
propagated by the relative rotation of the residues at the {\alpha}1{\beta}2
and {\alpha}2{\beta}1 interface.Comment: Reprinted (adapted) with permission from J. Phys. Chem. B
DOI:10.1021/jp3022908. Copyright (2012) American Chemical Societ
Photosensitized Singlet Oxygen Luminescence from the Protein Matrix of Zn-Substituted Myoglobin
A nanosecond laser near-infrared
spectrometer was used to study
singlet oxygen (<sup>1</sup>O<sub>2</sub>) emission in a protein matrix.
Myoglobin in which the intact heme is substituted by Zn-protoporphyrin
IX (ZnPP) was employed. Every collision of ground state molecular
oxygen with ZnPP in the excited triplet state results in <sup>1</sup>O<sub>2</sub> generation within the protein matrix. The quantum yield
of <sup>1</sup>O<sub>2</sub> generation was found to be equal to 0.9
± 0.1. On the average, six from every 10 <sup>1</sup>O<sub>2</sub> molecules succeed in escaping from the protein matrix into the solvent.
A kinetic model for <sup>1</sup>O<sub>2</sub> generation within the
protein matrix and for a subsequent <sup>1</sup>O<sub>2</sub> deactivation
was introduced and discussed. Rate constants for radiative and nonradiative <sup>1</sup>O<sub>2</sub> deactivation within the protein were determined.
The first-order radiative rate constant for <sup>1</sup>O<sub>2</sub> deactivation within the protein was found to be 8.1 ± 1.3 times
larger than the one in aqueous solutions, indicating the strong influence
of the protein matrix on the radiative <sup>1</sup>O<sub>2</sub> deactivation.
Collisions of singlet oxygen with each protein amino acid and ZnPP
were assumed to contribute independently to the observed radiative
as well as nonradiative rate constants