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Journal ArticleDOI

Influence of globin structure on the state of the heme. II. Allosteric transitions in methemoglobin.

07 May 1974-Biochemistry (American Chemical Society)-Vol. 13, Iss: 10, pp 2174-2186
About: This article is published in Biochemistry.The article was published on 1974-05-07. It has received 275 citations till now. The article focuses on the topics: Methemoglobin & Globin.
Citations
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Book ChapterDOI
TL;DR: Circular dichroism is a spectroscopic method which depends on the fact that certain molecules interact differently with right and left circularly polarized light and can provide information about the secondary structure of proteins and nucleic acids and about the binding of ligands to these types of macromolecule.
Abstract: Publisher Summary Circular dichroism (CD) is a spectroscopic method which depends on the fact that certain molecules interact differently with right and left circularly polarized light. Circularly polarized light is chiral—that is, it occurs in two nonsuperimposable forms that are mirror images of one another. To discriminate between the two chiral forms of light, a molecule must be chiral, including the vast majority of biological molecules. A method that can discern the subtle differences between non superimposable mirror image molecules (enantiomers) must be highly sensitive to the three-dimensional features of molecules—that is, to conformation. Binding of ligands or protein-protein and protein–DNA interactions can also alter the circular dichroism spectrum of the protein and/or nucleic acid. These changes in CD can be used to determine equilibrium constants, and they can also provide evidence for conformational changes. Thus, CD can provide information about the secondary structure of proteins and nucleic acids and about the binding of ligands to these types of macromolecule.

941 citations

Journal ArticleDOI
TL;DR: The overall quaternary structure of oxyhaemoglobin is identical, within experimental error, to that of carbon monoxide haemoglobin, and thus confirms the applicability of the allosteric mechanisms proposed by Perutz and Baldwin & Chothia to the process of oxygen binding.

578 citations

Journal ArticleDOI
03 Jan 1992-Science
TL;DR: This work has revealed that the allosteric mechanism is controlled by a previously unrecognized symmetry feature: quaternary switching from form T to form R occurs whenever heme-site binding creates a tetramer with at least one ligated subunit on each dimeric half-molecule.
Abstract: Although tetrameric hemoglobin has been studied extensively as a prototype for understanding mechanisms of allosteric regulation, the functional and structural properties of its eight intermediate ligation forms have remained elusive. Recent experiments on the energetics of cooperativity of these intermediates, along with assignments of their quaternary structures, have revealed that the allosteric mechanism is controlled by a previously unrecognized symmetry feature: quaternary switching from form T to form R occurs whenever heme-site binding creates a tetramer with at least one ligated subunit on each dimeric half-molecule. This "symmetry rule" translates the configurational isomers of heme-site ligation into six observed switchpoints of quaternary transition. Cooperativity arises from both "concerted" quaternary switching and "sequential" modulation of binding within each quaternary form, T and R. Binding affinity is regulated through a hierarchical code of tertiary-quaternary coupling that includes the classical allosteric models as limiting cases.

309 citations

Journal ArticleDOI
TL;DR: The interaction of hemoglobin with the synthetic peptide AcM-E-E, corresponding to the first 11 residues of band 3, and with the entire 43,000-Da cytoplasmic domain of the protein is reported, indicating that the peptide binds preferentially to deoxyhemoglobin.

293 citations

Journal ArticleDOI
TL;DR: Thioltransferase (glutaredoxin) appears to be specific for glutathione-containing mixed disulfides, and in separate experiments, TTase from rat liver displayed analogous selectivity.
Abstract: To study the substrate specificity and mechanism of thioltransferase (TTase) catalysis, we have used 14C- and 35S-radiolabeled mixed disulfides of cysteine and glutathione (GSH) with various cysteine-containing proteins. These protein mixed disulfide substrates were incubated with glutathione, glutathione disulfide (GSSG) reductase, and NADPH in the presence or absence of thioltransferase. Glutathione-dependent reduction of protein mixed disulfides was monitored both by release of trichloroacetic acid soluble radiolabel and by formation of GSSG in an NADPH-linked spectrophotometric assay. GSH-dependent dethiolation of [35S]glutathione-papain mixed disulfide (papain-SSG) and the corresponding bovine serum albumin mixed disulfide (BSA-SSG) were catalyzed by thioltransferase (from human red blood cells) as shown by the radiolabel assay, and equivalent rates were measured by the spectrophotometric assay. Dethiolation of [35S]hemoglobin-glutathione mixed disulfide (Hb-SSG) was also catalyzed by TTase. In contrast, TTase did not catalyze GSH-dependent dethiolation of [14C]papain-SScysteine or [14C]BSA-SScysteine as measured by the radiolabel assay. [14C]Hb-SScysteine and Hb-SScysteamine also did not serve as substrates. In separate experiments, TTase from rat liver displayed analogous selectivity. Thus, thioltransferase (glutaredoxin) appears to be specific for glutathione-containing mixed disulfides. Apparent TTase catalysis of GSSG formation from the papain- and BSA-SScysteine mixed disulfides was observed by the spectrophotometric assay, but a lag phase occurred consistent with preenzymatic formation of GSScysteine which could serve as the actual TTase substrate. Two-substrate kinetic studies of TTase with GSH and GSScysteine gave patterns of parallel lines on double-reciprocal plots (1/V vs 1/[S]), consistent with a simple ping-pong mechanism involving a TTase-SSG intermediate.

293 citations

References
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Journal ArticleDOI
19 May 1972-Nature
TL;DR: DPG has a two-fold effect on human deoxyhaemoglobin: it both stabilizes and slightly distorts the S form, and may therefore affect the solubility.
Abstract: DPG has a two-fold effect on human deoxyhaemoglobin. It both stabilizes and slightly distorts the S form, and may therefore affect the solubility.

671 citations

Journal ArticleDOI
30 Jun 1972-Nature
TL;DR: Dr Perutz describes how spin changes that accompany reaction with ligands alter the oxygen affinity of the haems.
Abstract: Haem-haem interaction consists of a change of tension at the haems, caused by a transition between two alternative quaternary structures of the protein. Dr Perutz describes how spin changes that accompany reaction with ligands alter the oxygen affinity of the haems.

334 citations

Journal ArticleDOI
TL;DR: Results suggest that the N-terminal amino groups of the non-α-chains are involved in the binding of 2,3-DPG to hemoglobin.
Abstract: Oxygen equilibria were measured on a number of human hemoglobins, which had been “stripped” of organic phosphates and isolated by column chromatography. In the presence of 2 × 10-4 M 2,3-diphosphoglycerate (2,3-DPG), the P50 of hemoglobins A, A2, S, and C increased about twofold, signifying a substantial and equal decrease in oxygen affinity. Furthermore, hemoglobins Chesapeake and MMilwaukee-1 which have intrinsically high and low oxygen affinities, respectively, also showed a twofold increase in P50 in the presence of 2 × 10-4 M 2,3-DPG. In comparison to these, hemoglobins AIC and F were less reactive with 2,3-DPG while hemoglobin FI showed virtually no reactivity. The N-terminal amino of each β-chain of hemoglobin AIC is linked to a hexose. In hemoglobin FI the N-terminal amino of each γ-chain is acetylated. These results suggest that the N-terminal amino groups of the non-α-chains are involved in the binding of 2,3-DPG to hemoglobin.

316 citations