Mycobacterial and Human Ferrous Nitrobindins: Spectroscopic and Reactivity Properties

Structural and functional properties of ferrous Mycobacterium tuberculosis (Mt-Nb) and human (Hs-Nb) nitrobindins (Nbs) were investigated. At pH 7.0 and 25.0 °C, the unliganded Fe(II) species is penta-coordinated and unlike most other hemoproteins no pH-dependence of its coordination was detected over the pH range between 2.2 and 7.0. Further, despite a very open distal side of the heme pocket (as also indicated by the vanishingly small geminate recombination of CO for both Nbs), which exposes the heme pocket to the bulk solvent, their reactivity toward ligands, such as CO and NO, is significantly slower than in most hemoproteins, envisaging either a proximal barrier for ligand binding and/or crowding of H2O molecules in the distal side of the heme pocket which impairs ligand binding to the heme Fe-atom. On the other hand, liganded species display already at pH 7.0 and 25 °C a severe weakening (in the case of CO) and a cleavage (in the case of NO) of the proximal Fe-His bond, suggesting that the ligand-linked movement of the Fe(II) atom onto the heme plane brings about a marked lengthening of the proximal Fe-imidazole bond, eventually leading to its rupture. This structural evidence is accompanied by a marked enhancement of both ligands dissociation rate constants. As a whole, these data clearly indicate that structural–functional relationships in Nbs strongly differ from what observed in mammalian and truncated hemoproteins, suggesting that Nbs play a functional role clearly distinct from other eukaryotic and prokaryotic hemoproteins.

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Ligand binding kinetics and dissociation of the human embryonic haemoglobins

Biochemical Journal ◽

10.1042/bj3150065 ◽

1996 ◽

Vol 315 (1) ◽

pp. 65-70 ◽

Cited By ~ 10

Author(s):

Oliver HOFMANN ◽

Thomas BRITTAIN

Keyword(s):

Ligand Binding ◽

Flash Photolysis ◽

Ph Dependence ◽

Equilibrium Constants ◽

General Scheme ◽

Dissociation Rate ◽

Oxygen Binding ◽

Dissociation Kinetics ◽

Oxygen Dissociation ◽

Dissociation Rate Constants

The three human embryonic haemoglobins have been studied using a range of stopped-flow and flash photolysis experiments. The association and dissociation kinetics and equilibrium constants for the tetramer–dimer reactions of the deoxy and oxygenated forms have been investigated and found to be characterized by constants similar to those of the human adult protein. The rates of oxygen dissociation from the embryonic haemoglobins have been measured and appear to be responsible for the high oxygen-binding affinity associated with the embryonic proteins compared with the adult protein. The pH dependence of the oxygen dissociation rate constants also accounts for the rather unusual, previously described, Bohr effects characteristic of the embryonic haemoglobins. A general scheme has been developed coupling both the dimer–tetramer equilibria and ligand-binding steps observed following photolysis of the liganded forms of the human embryonic haemoglobins.

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Computer simulations of the kinetics of reversible ligand binding to a multivalent macromolecule. Consequences of negative binding co-operativity associated with changes of the association and dissociation rate constants

Journal of Theoretical Biology ◽

10.1016/0022-5193(80)90323-9 ◽

1980 ◽

Vol 85 (3) ◽

pp. 497-505 ◽

Cited By ~ 1

Author(s):

Philip W. Kuchel ◽

Keith Dalziel

Keyword(s):

Ligand Binding ◽

Computer Simulations ◽

Rate Constants ◽

Dissociation Rate ◽

Dissociation Rate Constants ◽

Kinetics Of

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Dissociation rate constants and fractional binding of tracer estimated for three antibody populations in unstripped and stripped antiserum

Scandinavian Journal of Clinical and Laboratory Investigation ◽

10.3109/00365517909106096 ◽

1979 ◽

Vol 39 (3) ◽

pp. 215-221 ◽

Cited By ~ 4

Author(s):

V. Kruse

Keyword(s):

Rate Constants ◽

Dissociation Rate ◽

Dissociation Rate Constants

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Faculty Opinions recommendation of Measuring dissociation rate constants of protein complexes through subunit exchange: experimental design and theoretical modeling.

Faculty Opinions – Post-Publication Peer Review of the Biomedical Literature ◽

10.3410/f.724167923.793532861 ◽

2017 ◽

Author(s):

Michael Doyle

Keyword(s):

Experimental Design ◽

Rate Constants ◽

Protein Complexes ◽

Dissociation Rate ◽

Theoretical Modeling ◽

Subunit Exchange ◽

Dissociation Rate Constants

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Recombination-dissociation rate constants of acids, determined from polarographic data

Collection of Czechoslovak Chemical Communications ◽

10.1135/cccc19654150 ◽

1965 ◽

Vol 30 (12) ◽

pp. 4150-4167 ◽

Cited By ~ 3

Author(s):

Ya. I. Turyan

Keyword(s):

Rate Constants ◽

Dissociation Rate ◽

Dissociation Rate Constants

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Electroanalytical chemistry of vanadium complexes: Electrochemical oxidation of [V(IV)O(nta)(H2O)]-

Collection of Czechoslovak Chemical Communications ◽

10.1135/cccc19890064 ◽

1989 ◽

Vol 54 (1) ◽

pp. 64-69 ◽

Cited By ~ 4

Author(s):

Roland Meier ◽

Gerhard Werner ◽

Matthias Otto

Keyword(s):

Cyclic Voltammetry ◽

Electrochemical Oxidation ◽

Ph Dependence ◽

Differential Pulse ◽

Nitrilotriacetic Acid ◽

Reduced Form ◽

Vanadium Complexes ◽

Differential Pulse Polarography ◽

Electroanalytical Chemistry ◽

Ph Range

Electrochemical oxidation of [V(IV)O(nta)(H2O)]- (H3nta nitrilotriacetic acid) was studied in aqueous solution by means of cyclic voltammetry, differential pulse polarography, and current sampled DC polarography on mercury as electrode material. In the pH-range under study (5.5-9.0) the corresponding V(V) complex is produced by one-electron oxidation of the parent V(IV) species. The oxidation product is stable within the time scale of cyclic voltammetry. The evaluation of the pH-dependence of the half-wave potentials leads to a pKa value for [V(IV)O(nta)(H2O)]- which is in a good agreement with previous determinations. The measured value for E1/2 is very close to the formal potential E0 calculated via the Nernst equation on the basis of known literature values for log Kox and log Kred, the complex stability constants for the oxidized and reduced form, respectively.

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Hemoglobins of the tadpole of the bullfrog, Rana catesbeiana. pH dependence of ligand binding and subunit dissociation equilibria and kinetics.

Journal of Biological Chemistry ◽

10.1016/s0021-9258(18)50772-9 ◽

1979 ◽

Vol 254 (9) ◽

pp. 3393-3400

Author(s):

D H Atha ◽

A Riggs ◽

J Bonaventura ◽

C Bonaventura

Keyword(s):

Ligand Binding ◽

Rana Catesbeiana ◽

Ph Dependence ◽

Subunit Dissociation

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Desensitization Contributes to the Synaptic Response of Gain-of-Function Mutants of the Muscle Nicotinic Receptor

The Journal of General Physiology ◽

10.1085/jgp.200609570 ◽

2006 ◽

Vol 128 (5) ◽

pp. 615-627 ◽

Cited By ~ 23

Author(s):

Sergio Elenes ◽

Ying Ni ◽

Gisela D. Cymes ◽

Claudio Grosman

Keyword(s):

Nicotinic Receptor ◽

Dissociation Rate ◽

Gain Of Function ◽

Naturally Occurring ◽

Channel Opening ◽

Speed Up ◽

High Concentrations ◽

Dissociation Rate Constants ◽

Kinetics Of ◽

Peak Value

Although the muscle nicotinic receptor (AChR) desensitizes almost completely in the steady presence of high concentrations of acetylcholine (ACh), it is well established that AChRs do not accumulate in desensitized states under normal physiological conditions of neurotransmitter release and clearance. Quantitative considerations in the framework of plausible kinetic schemes, however, lead us to predict that mutations that speed up channel opening, slow down channel closure, and/or slow down the dissociation of neurotransmitter (i.e., gain-of-function mutations) increase the extent to which AChRs desensitize upon ACh removal. In this paper, we confirm this prediction by applying high-frequency trains of brief (∼1 ms) ACh pulses to outside-out membrane patches expressing either lab-engineered or naturally occurring (disease-causing) gain-of-function mutants. Entry into desensitization was evident in our experiments as a frequency-dependent depression in the peak value of succesive macroscopic current responses, in a manner that is remarkably consistent with the theoretical expectation. We conclude that the comparatively small depression of the macroscopic currents observed upon repetitive stimulation of the wild-type AChR is due, not to desensitization being exceedingly slow but, rather, to the particular balance between gating, entry into desensitization, and ACh dissociation rate constants. Disruption of this fine balance by, for example, mutations can lead to enhanced desensitization even if the kinetics of entry into, and recovery from, desensitization themselves are not affected. It follows that accounting for the (usually overlooked) desensitization phenomenon is essential for the correct interpretation of mutagenesis-driven structure–function relationships and for the understanding of pathological synaptic transmission at the vertebrate neuromuscular junction.

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