The Kinetic Activation Volumes for the Binding of Iodide to Cobalamin (Vitamin B12) Studied on a High Pressure Laser Temperature Jump Apparatus

1974 ◽  
Vol 52 (6) ◽  
pp. 910-914 ◽  
Author(s):  
Brian B. Hasinoff
Keyword(s):  
High Pressure ◽  
Metal Ion ◽  
Temperature Jump ◽  
Outer Sphere ◽  
Dissociation Rate ◽  
Vitamin B ◽  
Laser Temperature Jump ◽  
Dissociation Rate Constants ◽  
Kinetics Of ◽  
Activated Complex

The relaxation kinetics of the reaction of iodide with cobalamin (vitamin B12) were studied on a high pressure laser temperature jump apparatus in aqueous solution at 25° and ionic strength 0.2 M. Analysis of the pressure dependence of the formation and dissociation rate constants gave their respective volumes of activation to be: ΔVf* = 5.50 ± 0.8 cm3 mol−1 and ΔVd* = 11.5 ± 1.6 cm3 mol−1 The positive activation volume for formation of the complex, ΔVf*, after appropriate correction for the volume change due to formation of an outer sphere complex, is consistent with a dissociative type mechanism in which the metal ion – water bond is stretched in the activated complex.

Fast reaction kinetics of the binding of bromide to iron(III) studied on a high pressure laser temperature jump apparatus

1979 ◽  
Vol 57 (1) ◽  
pp. 77-82 ◽  
Author(s):  
Brian B. Hasinoff
Keyword(s):  
High Pressure ◽  
Activation Volume ◽  
Temperature Jump ◽  
Ion Pairs ◽  
Order Rate Constant ◽  
Fast Reaction ◽  
First Order ◽  
Laser Temperature Jump ◽  
Kinetics Of ◽  
Inner Sphere Complexes

The kinetics of the binding of Br− to Fe(III) were studied as a function of [H+] and [Br−] on a high pressure laser temperature jump apparatus up to 2.76 kbar. At constant [H+] the pseudo first order rate constant for formation of FeBr2+ showed little dependence on pressure or on [Br−] over the range 0.02 to 1.9 M. The results were interpreted by a mechanism in which Fe3+ and FeOH2+ react with Br− to form ion pairs prior to formation of their inner sphere complexes. The kinetic activation volume for the conversion of the Fe3+, Br− ion pair to FeBr2+ appears to be quite negative, consistent with an associative interchange (Ia) mechanism.

The kinetic activation volumes for the binding of chloride to iron(III), studied by means of a high pressure laser temperature jump apparatus

1976 ◽  
Vol 54 (11) ◽  
pp. 1820-1826 ◽  
Author(s):  
Brian B. Hasinoff
Keyword(s):  
High Pressure ◽  
Activation Volume ◽  
Temperature Jump ◽  
Relaxation Method ◽  
Laser Temperature Jump ◽  
Kinetics Of

The volumes of activation for the kinetics of the reaction of Cl− with Fe3+ and FeOH2+ have been determined by a laser temperature jump relaxation method at pressures up to 2.76 kbar. The results indicate that the two species, FeOH2+ and Fe3+, react with Cl− by different mechanisms. The activation volume for the binding of Cl− to FeOH2+ is positive (7.8 ± 1.0 cm3 mol−1), which is consistent with a dissociative interchange mechanism. The activation volume for the binding of Cl−1 to Fe3+ is negative (–4.5 ± 1.1 cm3 mol−1), which is consistent with an associative interchange mechanism.

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

2006 ◽  
Vol 128 (5) ◽  
pp. 615-627 ◽  
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.

scholarly journals Oversized galactosides as a probe for conformational dynamics in LacY

2018 ◽  
Vol 115 (16) ◽  
pp. 4146-4151 ◽  
Author(s):  
Irina Smirnova ◽  
Vladimir Kasho ◽  
Xiaoxu Jiang ◽  
Hong-Ming Chen ◽  
Stephen G. Withers ◽  
...  
Keyword(s):  
Binding Site ◽  
Conformational Dynamics ◽  
Dissociation Rate ◽  
Binding Kinetics ◽  
Lactose Permease ◽  
E Coli ◽  
Open Conformation ◽  
Dissociation Rate Constants ◽  
Kinetics Of ◽  
Micromolar Range

Binding kinetics of α-galactopyranoside homologs with fluorescent aglycones of different sizes and shapes were determined with the lactose permease (LacY) of Escherichia coli by FRET from Trp151 in the binding site of LacY to the fluorophores. Fast binding was observed with LacY stabilized in an outward-open conformation (kon = 4–20 μM−1·s−1), indicating unobstructed access to the binding site even for ligands that are much larger than lactose. Dissociation rate constants (koff) increase with the size of the aglycone so that Kd values also increase but remain in the micromolar range for each homolog. Phe27 (helix I) forms an apparent constriction in the pathway for sugar by protruding into the periplasmic cavity. However, replacement of Phe27 with a bulkier Trp does not create an obstacle in the pathway even for large ligands, since binding kinetics remain unchanged. High accessibility of the binding site is also observed in a LacY/nanobody complex with partially blocked periplasmic opening. Remarkably, E. coli expressing WT LacY catalyzes transport of α- or β-galactopyranosides with oversized aglycones such as bodipy or Aldol518, which may require an extra space within the occluded intermediate. The results confirm that LacY specificity is strictly directed toward the galactopyranoside ring and also clearly indicate that the opening on the periplasmic side is sufficiently wide to accommodate the large galactoside derivatives tested here. We conclude that the actual pathway for the substrate entering from the periplasmic side is wider than the pore diameter calculated in the periplasmic-open X-ray structures.

Electrode kinetics of Eu3+/Eu2+ reaction by cyclic voltammetry

1982 ◽  
Vol 47 (7) ◽  
pp. 1773-1779 ◽  
Author(s):  
T. P. Radhakrishnan ◽  
A. K. Sundaram
Keyword(s):  
Electron Transfer ◽  
Rate Constants ◽  
Outer Sphere ◽  
Electrode Reaction ◽  
Transfer Reactions ◽  
Cyclic Voltammetric ◽  
Edta Solution ◽  
Kinetics Of ◽  
Activated Complex ◽  
Good Agreement

The paper is a detailed study of the cyclic voltammetric behaviour of Eu3+ at HMDE in molar solutions of KCl, KBr, KI, KSCN and in 0.1M-EDTA solution with an indigenously built equipment. The computed values of the rate constants at various scan rates show good agreement with those reported by other electrochemical methods. In addition, the results indicate participation of a bridged activated complex in the electron-transfer step, the rate constants showing the trend SCN- > I- > Br- > Cl- usually observed for bridging order of these anions in homogeneous electron-transfer reactions. The results for Eu-EDTA system, however, indicate involvement of an outer sphere activated complex in the electrode reaction.

Laser Temperature Jump Study of the Helix⇌Coil Kinetics of an Alanine Peptide Interpreted with a ‘Kinetic Zipper' Model

Biochemistry ◽  
1997 ◽  
Vol 36 (30) ◽  
pp. 9200-9210 ◽  
Author(s):  
Peggy A. Thompson ◽  
William A. Eaton ◽  
James Hofrichter
Keyword(s):  
Temperature Jump ◽  
Laser Temperature Jump ◽  
Kinetics Of

Calculated R.R.K.M. unimolecular dissociation rate constants for hydrazine

1969 ◽  
Vol 47 (14) ◽  
pp. 2593-2599 ◽  
Author(s):  
D. W. Setser ◽  
W. C. Richardson
Keyword(s):  
Experimental Data ◽  
Lower Bounds ◽  
Rate Constants ◽  
Chemical Activation ◽  
Dissociation Rate ◽  
Upper And Lower Bounds ◽  
Unimolecular Dissociation ◽  
Complex Models ◽  
Dissociation Rate Constants ◽  
Activated Complex

Unimolecular rate constants for hydrazine dissociation by thermal and chemical activation have been calculated according to the R.R.K.M. theory. The two activated complex models used in the calculations represent plausible upper and lower bounds to the rate constants. The calculations are mainly directed toward establishing expected decomposition to stablilization ratios of N2H4 produced by combination of NH2 radicals; however, a general comparison to available experimental data for hydrazine dissociation is made.

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