Experimental31p nmr study of the influence of ionic strength on the apparent dissociation constant of mgatp

1994 ◽  
Vol 2 (2) ◽  
pp. 101-107 ◽  
Author(s):  
I. Mottet ◽  
R. Demeure ◽  
B. Gallez ◽  
C. Grandin ◽  
B. E. Van Beers ◽  
...  
Keyword(s):  
Ionic Strength ◽  
Dissociation Constant ◽  
Apparent Dissociation Constant ◽  
Nmr Study

Binding of adenylosuccinate synthetase to contractile proteins of muscle

1989 ◽  
Vol 257 (1) ◽  
pp. C29-C35 ◽  
Author(s):  
J. P. Manfredi ◽  
R. Marquetant ◽  
A. D. Magid ◽  
E. W. Holmes
Keyword(s):  
Ionic Strength ◽  
Dissociation Constant ◽  
Thin Filament ◽  
Contractile Proteins ◽  
Purine Nucleotide ◽  
Apparent Dissociation Constant ◽  
Thin Filaments ◽  
Adenylosuccinate Synthetase ◽  
Purine Nucleotide Cycle ◽  
Low Ionic Strength

The muscle isozyme of adenylosuccinate synthetase (AdSS), an enzyme of the purine nucleotide cycle, has previously been shown to bind to purified F-actin in buffers of low ionic strength and pH (Ogawa et al. Eur. J. Biochem. 85: 331-338, 1978). We have extended these observations by measuring the association of both crude and purified AdSS with the contractile proteins of muscle in buffers of physiological ionic strength and pH. Under these conditions, the enzyme binds to F-actin, actin-tropomyosin complexes, reconstructed thin filaments, and myofibrils but not to myosin. The apparent dissociation constant of 1.2 microM and binding maximum of 2.6 nmol enzyme/mg myofibrils indicate that binding of AdSS to myofibrils can be physiologically significant. The results suggest that AdSS in muscle may be associated with the thin filament of myofibrils.

Which value for the first dissociation constant of carbonic acid should be used in biological work?

1991 ◽  
Vol 260 (5) ◽  
pp. C1113-C1116 ◽  
Author(s):  
R. W. Putnam ◽  
A. Roos
Keyword(s):  
Ionic Strength ◽  
Activity Coefficient ◽  
Dissociation Constant ◽  
Carbonic Acid ◽  
Mass Action ◽  
Bicarbonate Concentration ◽  
Apparent Dissociation Constant ◽  
Logarithmic Form ◽  
Ion Activity ◽  
Hasselbalch Equation

The apparent first dissociation constant of carbonic acid has been defined in different ways in the literature. Harned and co-workers (8-10) have defined it in terms of molalities of the participating species, including H ions: Ks = mHmHCO3/mCO2. In contrast, Hastings and Sendroy have defined an apparent constant in which acidity is expressed as H ion activity: K'1 = aHmHCO3/mCO2. These constants differ by a factor gamma H, the activity coefficient of H ions at the prevailing ionic strength. Therefore, pK'1 is greater than pKs by an amount equal to -log gamma H, which, at mu = 0.16 M, is approximately 0.1. It is important that the correct value for the apparent dissociation constant or its logarithmic form be entered in the mass action expression or in the Henderson-Hasselbalch equation in order to prevent significant errors in the computation by means of these equations of quantities that cannot be directly measured. Specifically, for the derivation of bicarbonate concentration from PCO2 and pH (-log aH), pK'1 is to be used and not an uncorrected pKs.

The Physiology of Carbon Dioxide Transport in Insect Blood

1950 ◽  
Vol 27 (2) ◽  
pp. 158-174 ◽  
Author(s):  
L. LEVENBOOK
Keyword(s):  
Carbon Dioxide ◽  
Dissociation Constant ◽  
Temperature Coefficient ◽  
Carbonic Acid ◽  
Apparent Dissociation Constant ◽  
Carbon Dioxide Transport ◽  
High Co2 ◽  
The Third ◽  
A Value ◽  
Dissociation Curves

1. The pH of the blood of the third instar Gastrophilus larva is 6.64 at 38° C. with a pH-temperature coefficient of -0.007 Per 1° C. rise in temperature. 2. The total CO2 content of the blood varies from 40.6 to 131.4 vol. % with an average of 72.4 vol. %. The CO2 content of the tissues minus the cuticle is very close to, and follows the variations in, the CO2 content of the blood. 3. The CO2 tension in the blood is from 300 to 500 mm. Hg. From 30 to 50% of the CO2 is in solution, the rest in the form of bicarbonate. Carbamate formation does not occur in the blood. 4. The ‘apparent’ dissociation constant for carbonic acid, (pK'1), has a value of 6.08 (S.D. ±0.06) at 38° C. and 6.19 (s.d. ±0.13) at 16° C. 5. CO2 dissociation curves have been drawn for 38 and 16° C. The slope of the curves indicates that the whole of the CO2 is given off at zero CO2 tension, and that the blood is adapted for functioning at high CO2 tensions.

Characterization of a Hyperpolarization-Activated Inward Current in Cajal-Retzius Cells in Rat Neonatal Neocortex

2000 ◽  
Vol 84 (3) ◽  
pp. 1681-1691 ◽  
Author(s):  
Werner Kilb ◽  
Heiko J. Luhmann
Keyword(s):  
Dissociation Constant ◽  
Reversal Potential ◽  
Hill Coefficient ◽  
Resting Membrane Potential ◽  
Patch Clamp Technique ◽  
Apparent Dissociation Constant ◽  
Membrane Hyperpolarization ◽  
Whole Cell ◽  
Inward Current ◽  
Retzius Cells

Cajal-Retzius cells are among the first neurons appearing during corticogenesis and play an important role in the establishment of cortical lamination. To characterize the hyperpolarization-activated inward current ( I h) and to investigate whether I h contributes to the relatively positive resting membrane potential (RMP) of these cells, we analyzed the properties of I h in visually identified Cajal-Retzius cells in cortical slices from neonatal rats using the whole cell patch-clamp technique. Membrane hyperpolarization to −90 mV activated a prominent inward current that was inhibited by 1 mM Cs+ and was insensitive to 1 mM Ba2+. The activation time constant for I h was strongly voltage dependent. In Na+-free solution, I h was reduced, indicating a contribution of Na+. An analysis of the tail currents revealed a reversal potential of −45.2 mV, corresponding to a permeability coefficient (pNa+/pK+) of 0.13. While an increase in the extracellular K+ concentration ([K+]e) enhances I h, it was reduced by a [K+]e decrease. This [K+]e dependence could not be explained by an effect on the electromotive force on K+ but suggested an additional extracellular binding site for K+ with an apparent dissociation constant of 7.2 mM. Complete Cl−substitution by Br−, I−, or NO3 − had no significant effect on I h, whereas a complete Cl−substitution by the organic compounds methylsulfate, isethionate, or gluconate reduced I h by ∼40%. The I h reduction observed in gluconate could be abolished by the addition of Cl−. The analysis of the [Cl−]e dependence of I h revealed a dissociation constant of 9.8 mM and a Hill-coefficient of 2.5, while the assumption of a gluconate-dependent I h reduction required an unreasonably high Hill-coefficient >20. An internal perfusion with the lidocaine derivative lidocaine N-ethyl bromide blocks I h within 1 min after establishment of the whole cell configuration. An inhibition of I h by 1 mM Cs+ was without an effect on RMP, action potential amplitude, threshold, width, or afterhyperpolarization. We conclude from these results that Cajal-Retzius cells express a prominent I hwith characteristic properties that does not contribute to the RMP.

scholarly journals Benzoate Decreases the Binding of cis,cis-Muconate to the BenM Regulator despite the Synergistic Effect of Both Compounds on Transcriptional Activation

2004 ◽  
Vol 186 (4) ◽  
pp. 1200-1204 ◽  
Author(s):  
Todd J. Clark ◽  
Robert S. Phillips ◽  
Becky M. Bundy ◽  
Cory Momany ◽  
Ellen L. Neidle
Keyword(s):  
Dna Binding ◽  
Synergistic Effect ◽  
Dissociation Constant ◽  
Transcriptional Activation ◽  
Emission Spectroscopy ◽  
Fluorescence Emission ◽  
Transcriptional Regulator ◽  
Dna Binding Domain ◽  
Apparent Dissociation Constant ◽  
High Level

ABSTRACT Fluorescence emission spectroscopy was used to investigate interactions between two effectors and BenM, a transcriptional regulator of benzoate catabolism. BenM had a higher affinity for cis,cis-muconate than for benzoate as the sole effector. However, the presence of benzoate increased the apparent dissociation constant (reduced the affinity) of the protein for cis,cis-muconate. Similar results were obtained with truncated BenM lacking the DNA-binding domain. High-level transcriptional activation may require that some monomers within a BenM tetramer bind benzoate and others bind cis,cis-muconate.

scholarly journals Charybdotoxin block of single Ca2+-activated K+ channels. Effects of channel gating, voltage, and ionic strength.

1988 ◽  
Vol 91 (3) ◽  
pp. 317-333 ◽  
Author(s):  
C S Anderson ◽  
R MacKinnon ◽  
C Smith ◽  
C Miller
Keyword(s):  
Ionic Strength ◽  
Plasma Membranes ◽  
Scorpion Venom ◽  
Dissociation Rate ◽  
K Channel ◽  
Single Channels ◽  
Association Rate ◽  
Open Probability ◽  
Apparent Dissociation Constant ◽  
K Channels

Charybdotoxin (CTX), a small, basic protein from scorpion venom, strongly inhibits the conduction of K ions through high-conductance, Ca2+-activated K+ channels. The interaction of CTX with Ca2+-activated K+ channels from rat skeletal muscle plasma membranes was studied by inserting single channels into uncharged planar phospholipid bilayers. CTX blocks K+ conduction by binding to the external side of the channel, with an apparent dissociation constant of approximately 10 nM at physiological ionic strength. The dwell-time distributions of both blocked and unblocked states are single-exponential. The toxin association rate varies linearly with the CTX concentration, and the dissociation rate is independent of it. CTX is competent to block both open and closed channels; the association rate is sevenfold faster for the open channel, while the dissociation rate is the same for both channel conformations. Membrane depolarization enhances the CTX dissociation rate e-fold/28 mV; if the channel's open probability is maintained constant as voltage varies, then the toxin association rate is voltage independent. Increasing the external solution ionic strength from 20 to 300 mM (with K+, Na+, or arginine+) reduces the association rate by two orders of magnitude, with little effect on the dissociation rate. We conclude that CTX binding to the Ca2+-activated K+ channel is a bimolecular process, and that the CTX interaction senses both voltage and the channel's conformational state. We further propose that a region of fixed negative charge exists near the channel's CTX-binding site.

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