Cation binding in wood: applications to understanding historical changes in divalent cation availability to red spruce

1990 ◽  
Vol 20 (12) ◽  
pp. 1840-1849 ◽  
Author(s):  
N. Momoshima ◽  
E. A. Bondietti
Keyword(s):  
Divalent Cation ◽  
Binding Sites ◽  
Cell Walls ◽  
Mineral Acid ◽  
Cation Binding ◽  
Red Spruce ◽  
Base Saturation ◽  
Ph Values ◽  
Spruce Wood ◽  
Alkaline Earths

The ion exchange characteristics of red spruce (Picearubens Sarg.) bolewood were investigated to understand factors that control divalent cation and H+ concentrations in tracheid cell walls. Vertical concentration measurements of selected cations along the stem demonstrated that the alkaline earths showed the expected chromatographic fractionation, while other cations showed variable patterns relative to calcium. The concentration of cation binding sites (pectates) decreased in a predictable manner from the pith towards the cambium as a function of radius, not chronological age, explaining why in red spruce calcium concentrations are usually highest in the oldest wood. Red spruce wood from Maine and Tennessee had divalent base saturations of about 60 to 65% before the mid-1900s; however, divalent base saturations increased to about 75 to 80% in the mid-1900s, after which they decreased. Wood pH values were highest when divalent base saturation was highest. Calcium and potassium equilibration experiments were conducted, and the results were used to parameterize the Donnan model of cation exchange to understand why base saturation in woody tissues changes in different time periods. Increased divalent cation concentrations in red spruce wood formed during the 1940s to the 1970s are explainable by small increases in both sap pH and divalent cation concentrations and may be the signal of cation mobilization following increasing mineral acid anion deposition from the atmosphere.

The divalent cation-binding sites of gramicidin A transmembrane ion-channel

Biopolymers ◽  
1991 ◽  
Vol 31 (4) ◽  
pp. 425-434 ◽  
Author(s):  
A. P. Golovanov ◽  
I. L. Barsukov ◽  
A. S. Arseniev ◽  
V. F. Bystrov ◽  
S. V. Sukhanov ◽  
...  
Keyword(s):  
Ion Channel ◽  
Divalent Cation ◽  
Binding Sites ◽  
Cation Binding ◽  
Gramicidin A

scholarly journals Effects of ATP on the Interaction of Ca++, Mg++, and K+ with Fragmented Sarcoplasmic Reticulum Isolated from Rabbit Skeletal Muscle

1967 ◽  
Vol 50 (5) ◽  
pp. 1327-1352 ◽  
Author(s):  
Arselio P. Carvalho ◽  
Barbara Leo
Keyword(s):  
Skeletal Muscle ◽  
Sarcoplasmic Reticulum ◽  
Binding Sites ◽  
Membrane Fraction ◽  
Binding Capacity ◽  
Cation Binding ◽  
The Other ◽  
Surface Binding ◽  
Ph Values ◽  
Number Of Binding Sites

Fragmented sarcoplasmic reticulum isolated from skeletal muscle of the rabbit has a cation-binding capacity of about 350 µeq/g of protein at neutral pH. The same binding sites bind Ca, Mg, K, and H ions and, consequently, the selective binding of Ca induced by ATP releases an amount of the other cations equivalent to the Ca taken up. At pH values below 6.2, an increasing number of binding sites are associated with H+, and ATP induces exchange of Ca mostly for H+. At pH values above 6.2, the binding sites exist in the form of Mg and K, and Ca is bound in exchange for these cations. The total bound Ca + Mg + K, expressed in microequivalents of cations bound per gram of protein, is approximately constant at various pCa values, which indicates a stoichiometric exchange of Ca for the other cations. To accomplish the same degree of exchange of Ca for other cations bound, in the absence of ATP, concentrations of free Ca++ of about 1000-fold higher than those needed in the presence of ATP are required in the medium. We cannot distinguish between a mechanism whereby Ca actively transported into a compartment of the microsomal vesicles containing also the binding sites is bound passively to these sites in exchange for Mg, K, and H and another in which ATP selectively increases the affinity of surface-binding sites for Ca. Irrespective of the mechanism of accumulation, the Ca retained does not contribute to the activity of the cation in the membrane fraction. Caffeine (10 mM) has no effect on the binding of Ca, but releases a more labile fraction of Ca, which presumably accumulates in excess of the bound Ca. Procaine (5 mM) antagonizes the effect of caffeine. Acetylcholine and epinephrine have no effect on the binding of Ca.

Characterization and location of divalent cation binding sites in bovine glial fibrillary acidic protein

Biochemistry ◽  
1988 ◽  
Vol 27 (18) ◽  
pp. 7045-7050 ◽  
Author(s):  
Zan Wei Yang ◽  
Chuang Fong Kong ◽  
Joseph A. Babitch
Keyword(s):  
Glial Fibrillary Acidic Protein ◽  
Divalent Cation ◽  
Binding Sites ◽  
Cation Binding ◽  
Acidic Protein

scholarly journals Divalent cation competition with [3H]saxitoxin binding to tetrodotoxin-resistant and -sensitive sodium channels. A two-site structural model of ion/toxin interaction.

1993 ◽  
Vol 101 (2) ◽  
pp. 153-182 ◽  
Author(s):  
D D Doyle ◽  
Y Guo ◽  
S L Lustig ◽  
J Satin ◽  
R B Rogart ◽  
...  
Keyword(s):  
Divalent Cation ◽  
Binding Sites ◽  
Structural Model ◽  
Divalent Cations ◽  
Ph Dependence ◽  
Monovalent Cation ◽  
Cation Binding ◽  
Na Channel ◽  
Na Channels ◽  
Ph Titration

Monovalent and divalent cations competitively displace tetrodotoxin and saxitoxin (STX) from their binding sites on nerve and skeletal muscle Na channels. Recent studies of cloned cardiac (toxin-resistant) and brain (toxin-sensitive) Na channels suggest important structural differences in their toxin and divalent cation binding sites. We used a partially purified preparation of sheep cardiac Na channels to compare monovalent and divalent cation competition and pH dependence of binding of [3H]STX between these toxin-resistant channels and toxin-sensitive channels in membranes prepared from rat brain. The effects of several chemical modifiers of amino acid groups were also compared. Toxin competition curves for Na+ in heart and Cd2+ in brain yielded similar KD values to measurements of equilibrium binding curves. The monovalent cation sequence for effectiveness of [3H]STX competition is the same for cardiac and brain Na channels, with similar KI values for each ion and slopes of -1. The effectiveness sequence corresponds to unhydrated ion radii. For seven divalent cations tested (Ca2+, Mg2+, Mn2+, Co2+, Ni2+, Cd2+, and Zn2+) the sequence for [3H]STX competition was also similar. However, whereas all ions displaced [3H]STX from cardiac Na channels at lower concentrations, Cd2+ and Zn2+ did so at much lower concentrations. In addition, and by way of explication, the divalent ion competition curves for both brain and cardiac channels (except for Cd2+ and Zn2+ in heart and Zn2+ in brain) had slopes of less than -1, consistent with more than one interaction site. Two-site curves had statistically better fits than one-site curves. The derived values of KI for the higher affinity sites were similar between the channel types, but the lower affinity KI's were larger for heart. On the other hand, the slopes of competition curves for Cd2+ and Zn2+ were close to -1, as if the cardiac Na channel had one dominant site of interaction or more than one site with similar values for KI. pH titration of [3H]STX binding to cardiac channels showed a pKa of 5.5 and a slope of 0.6-0.9, compared with a pKa of 5.1 and slope of 1 for brain channels. Tetramethyloxonium (TMO) treatment abolished [3H]STX binding to cardiac and brain channels and STX protected channels, but the TMO effect was less dramatic for cardiac channels. Trinitrobenzene sulfonate preferentially abolished [3H]STX binding to brain channels by action at an STX protected site.(ABSTRACT TRUNCATED AT 400 WORDS)

scholarly journals Divalent cation and chloride ion sites of chicken acid sensing ion channel 1a elucidated by x-ray crystallography

2018 ◽  
Author(s):  
Nate Yoder ◽  
Eric Gouaux
Keyword(s):  
Ion Channels ◽  
Divalent Cation ◽  
Binding Sites ◽  
Divalent Cations ◽  
Cation Binding ◽  
Ion Binding ◽  
X Ray ◽  
High Ph ◽  
X Ray Crystallography ◽  
Ion Binding Sites

AbstractAcid sensing ion channels (ASICs) are proton-gated ion channels that are members of the degenerin/epithelial sodium channel superfamily and are expressed throughout central and peripheral nervous systems. ASICs have been implicated in multiple physiological processes and are subject to numerous forms of endogenous and exogenous regulation that include modulation by Ca2+ and Cl− ions. However, the mapping of ion binding sites as well as a structure-based understanding of the mechanisms underlying ionic modulation of ASICs have remained elusive. Here we present ion binding sites of chicken ASIC1a in resting and desensitized states at high and low pH, respectively, determined by anomalous diffraction x-ray crystallography. The acidic pocket serves as a nexus for divalent cation binding at both low and high pH, while we observe divalent cation binding within the central vestibule on the resting channel at high pH only. Moreover, neutralization of residues positioned to coordinate divalent cations via individual and combined Glu to Gln substitutions reduced, but did not extinguish, modulation of proton-dependent gating by Ca2+. Additionally, we demonstrate that anion binding at the canonical thumb domain site is state-dependent and present a previously undetected anion site at the mouth of the extracellular fenestrations on the resting channel. Our results map anion and cation sites on ASICs across multiple functional states, informing possible mechanisms of modulation and providing a blueprint for the design of therapeutics targeting ASICs.

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