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Role of dimerization in the control of the functioning of the human haemoglobin mutant haemoglobin Howick (beta 37 Trp-->Gly).

ABSTRACT: Haemoglobin Howick shows a high oxygen affinity (p50 = 1 mmHg) and a low co-operativity (n = 1.3). Equilibrium studies show the protein to be essentially totally dimeric in the oxygenated form. A wide range of rapid kinetic experiments indicate that the deoxygenated form of the protein exists in a tetramer<-->dimer equilibrium with an associated equilibrium constant of 3 microM. These kinetic data also indicate that the oxygenated form of the protein exists in a tetramer<-->dimer equilibrium with an associated equilibrium constant of 35 mM, and furthermore clearly identifies a large increase in the rate of the tetramer-to-dimer dissociation process as the origin of the vastly increased dissociation equilibrium constants. Simulations of the protein-concentration-dependence of the oxygen-binding properties of haemoglobin Howick, based on the measured equilibrium parameters, closely fits the experimental data. The change in dimerization constant for the deoxygenated form of the protein corresponds remarkably well to the free-energy change predicted for the simple transfer of the amino acid side chain at position beta 37 from a hydrophobic to a hydrophilic environment during the dimerization process.

SUBMITTER: Brittain T

PROVIDER: S-EPMC1138197 | biostudies-other | 1994 Jun

REPOSITORIES: biostudies-other

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Light-induced conversion of Trp to Gly and Gly hydroperoxide in IgG1.

Project description:The exposure of IgG1 in aqueous solution to light with ? = 254 nm or ? > 295 nm yields products consistent with Trp radical cation formation followed by (?)C-(?)C cleavage of the Trp side chain. The resulting glycyl radicals either are reduced to Gly or add oxygen prior to reduction to Gly hydroperoxide. Photoirradiation at ? = 254 nm targets Trp at positions 191 (light chain), 309 and 377 (heavy chain) while photoirradiation at ? > 295 nm targets Trp at position 309 (heavy chain). Mechanistically, the formation of Trp radical cations likely proceeds via photoinduced electron or hydrogen transfer to disulfide bonds, yielding thiyl radicals and thiols, where thiols may serve as reductants for the intermediary glycyl or glycylperoxyl radicals.

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2023-01-25 | GSE206098 | GEO

The periplasmic cavity of LacY mutant Cys154?Gly: how open is open?

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