Search PubMed⌕ Search

SEARCH · Search PubMed

Results for “Cations”

Search indexed PubMed citations on genomics, clinical trials, systematic reviews and public health. Explore titles, authors and supplied subject terms, then open the PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 1,171 records · Page 65Linked to original sources
PubMed2005

Tuning of the alpha-terthiophene radical cation coupling reaction using mixed micelles with varying charge density.

The photophysics and photochemistry of alpha-terthiophene (alphaT), compartmentalized in mixed nonionic/anionic micelles, have been investigated with focus on the influence of the micellar surface charge density on the formation of the radical coupling product alpha-hexathiophene (alphaH). By varying the ratio of nonionic-to-anionic surfactants, and assuming ideal mixing, the charge density of the mixed micelles was varied. From Poisson-Boltzmann calculations, performed using the cell model, the electrostatic potential and the counterion activity were estimated as a function of the distance from the micellar surface. Upon excitation, the triplet state of alphaT is formed, from which the alphaT radical cation can be formed by absorption of a second photon. The radical cation can form alphaH if it encounters another alphaT radical cation. Under the experimental conditions used, this implies that the alphaH formation only occurs if the compartmentalized radical cation is able to migrate from its host micelle to another micelle, either via the surrounding bulk or by fusion of two micelles followed by mixing of their contents before micellar fission. The formation yield of the radical cation depends on the charge density of the mixed micelle; a lower charge density, that is, an increased amount of nonionic surfactant, lowers the yield. The yield of the coupling product alphaH, however, does not follow the same trend. A maximum yield of alphaH is found at intermediate nonionic surfactant molar ratios. This behavior is understood in terms of the Poisson-Boltzmann simulation results and by comparing charge-density changes as a function of molar fraction with the changes in counterion activity. The alphaH yield is a result of the balance between an increased possibility of radical cation bulk migration and a lowered electrostatic stabilization of the radical.

Journal Article↗
PubMed2006

Raman spectroscopy of short-lived terthiophene radical cations generated by photochemical and chemical oxidation.

The Raman spectra of various terthiophene radical cations are investigated; namely those of unsubstituted terthiophene and two styryl-substituted terthiophenes. Transient pump-probe resonance Raman spectroscopy is used to measure the short-lived radical cation spectra of non-end-capped 2,2':5',2''-terthiophene (3T) and 3'-[(E)-2-(4-nitrophenyl)ethenyl]-2,2':5',2''-terthiophene (NO2-pe3T). For these two compounds, the radical cations are generated via either direct photogeneration or photochemically using the electron acceptor tetracyanoethylene. The radical cation of 5,5''-dimethyl-3'-[(E)-2-phenylethenyl]-2,2':5',2''-terthiophene (DM-pe3T) is stable for up to five minutes as a result of the two alpha end caps and continuous-wave resonance Raman spectroscopy and chemical oxidation is used to obtain the spectrum of this radical cation. The resonance Raman spectra of all three terthiophene radical cations are dominated by a group of very intense bands in the low-frequency region. These bands have been assigned, by density functional theory methods, to C-S stretching modes coupled to thiophene ring deformations. These modes are significantly less intense in the sigma-dimer of NO2-pe3T [i.e. the corresponding styryl sexithiophene (NO2-pe3T)2]. This observation is attributed to a smaller change in the C--S bond order in the sexithiophene compared to the analogous terthiophene. This bond order difference may be rationalised by consideration of the singly occupied molecular orbital and lowest unoccupied molecular orbital, which are involved in the electronic transition probed by the laser excitation wavelength.

Journal Article↗
PubMed2004

Interaction between trypsinogen isoforms in genetically determined pancreatitis: mutation E79K in cationic trypsin (PRSS1) causes increased transactivation of anionic trypsinogen (PRSS2).

The human pancreas secretes two major trypsinogen isoforms, cationic and anionic trypsinogen. To date, 19 genetic variants have been identified in the cationic trypsinogen gene (PRSS1) of patients with hereditary, familial, or sporadic chronic pancreatitis. A common feature of cationic trypsinogen mutants studied so far is an increased propensity for autocatalytic activation (autoactivation). This is thought to lead to premature intrapancreatic digestive protease activation. In contrast, no pancreatitis-associated mutations have been found in the anionic trypsinogen gene (PRSS2), suggesting that this isoform might play a relatively unimportant role in pancreatitis. To challenge this notion, here we describe the unique properties of the E79K cationic trypsinogen mutation (c.235G>A), which was identified in three European families affected by sporadic or familial pancreatitis cases. In vitro analysis of recombinant wild-type and mutant enzymes revealed that catalytic activity of E79K trypsin was normal, and its inhibition by pancreatic secretory trypsin inhibitor was unaffected. Although the E79K mutation introduces a potential new tryptic cleavage site, autocatalytic degradation (autolysis) of E79K-trypsin was also unchanged. Furthermore, in contrast to previously characterized disease-causing mutations, E79K markedly inhibited autoactivation of cationic trypsinogen. Remarkably, however, E79K trypsin activated anionic trypsinogen two-fold better than wild-type cationic trypsin did, while the common pancreatitis-associated mutants R122H or N29I had no such effect. The observations not only suggest a novel mechanism of action for pancreatitis-associated trypsinogen mutations, but also highlight the importance of interactions between the two major trypsinogen isoforms in the development of genetically determined chronic pancreatitis.

Adult↗
PubMed2001

Enhanced invasiveness of pancreatic adenocarcinoma cells stably transfected with cationic trypsinogen cDNA.

Various studies have described increased expression of cationic trypsinogen in malignant tumor cells. To explore the role of secreted cationic trypsinogen in invasion by cancer cells, we introduced cationic trypsinogen cDNA into Panc-1, a pancreatic adenocarcinoma-derived cell line that lacks expression of endogeneous trypsinogen. Four independent clones (designated Panc-1-Try-7, -9, -11 and -24) stably expressing cationic trypsinogen mRNA were isolated and processed for further study. In a zymographic analysis, gelatinolytic activity for cationic trypsinogen was detectable in serum-free conditioned media obtained from all 4 transfectants but not in media from mock-transfected or parental Panc-1 cells. A Matrigel invasion assay revealed that all trypsinogen-expressing transfectants acquired significantly greater invasive ability than that shown by mock-transfected and parental Panc-1 cells. In addition, enhanced invasiveness of the transfectants was suppressed by FUT-175, a serine protease inhibitor, to the level seen in parental cells. These results provide direct evidence that cationic trypsinogen can increase the invasive ability of carcinoma cells.

Adenocarcinoma↗
PubMed1988

Regulatory volume decrease in alveolar macrophages: cation loss is not correlated with changes in membrane recycling.

Alveolar macrophages regain their normal volume after swelling in hypo-osmotic solutions. This process, termed regulatory volume decrease (RVD), is initiated 3-5 minutes after exposure of cells to hypo-osmotic solutions, and by 30 min, near-normal volumes are attained. Volume decrease does not occur at 0 degrees C or in solutions in which Na+ has been replaced by K+, or Cl- by the impermeant anion gluconate. These results, as well as direct measurement of intracellular cations, indicate that decreases in cell volume result primarily from the loss of K+ and Cl- and are similar to RVD in lymphocytes. Kinetic analysis of cation loss, both by directly measuring changes in intracellular cation content and by assaying rubidium efflux, showed that cation loss occurred immediately upon media dilution. The rate of cation loss fit first-order kinetics and preceded both the initiation of volume decrease and the maximum increase in surface receptor number. These results suggest that the cation transporters responsible for RVD are located at the cell surface and that regulation of activity is not dependent on alterations in membrane movement.

Animals↗
PubMed2002

Complexes of bivalent metal cations in electrospray mass spectra of common organic compounds.

In the standard electrospray ionization mass spectra of many common, low molecular mass organic compounds dissolved in methanol, peaks corresponding to ions with formula [3M + Met](2+) (M = organic molecule, Met = bivalent metal cation) are observed, sometimes with significant abundances. The most common are ions containing Mg(2+), Ca(2+) and Fe(2+). Their presence can be easily rationalized on the basis of typical organic reaction work-up procedures. The formation of [3M + Met](2+) ions has been studied using N-FMOC-proline methyl ester as a model organic ligand and Mg(2+), Ca(2+), Sr(2+), Ba(2+), Fe(2+), Ni(2+), Mn(2+), Co(2+) and Zn(2+) chlorides or acetates as the sources of bivalent cation. It was found that all ions studied form [3M + Met](2+) complexes with N-FMOC-proline methyl ester, some of them at very low concentrations. Transition metal cations generally show higher complexation activity in comparison with alkaline earth metal cations. They are also more specific in the formation of [3M + Met](2+) complexes. In the case of alkaline earth metal cations [2M + Met](2+) and [4M + Met](2+) complex ions are also observed. It has been found that [3M + Met](2+) complex ions undergo specific fragmentation at relatively low energy, yielding fluorenylmethyl cation as a major product. [M + Na](+) ions are much more stable and their fragmentation is not as specific.

Journal Article↗
PubMed2006

A study of gas-phase cationization in matrix-assisted laser desorption/ionization time-of-flight mass spectrometry.

A specially constructed split sample probe was used to unequivocally demonstrate that gas-phase cationization occurs within the desorption plume during a matrix-assisted laser desorption/ionization experiment. Two separate samples were prepared for analysis: on side A, a mixture of poly(ethylene glycol) (PEG) 1500 analyte and 2,5-dihydroxybenzoic acid (DHB) matrix, and on side B a mixture of DHB matrix and lithium hydroxide (LiOH), the cationization reagent. Analysis of the data showed that when the ionization laser was focused on the split (so that both sides were illuminated), Li(+)-cationized PEG peaks were observed. Since the PEG analyte did not come into contact with Li(+) in either the solution or solid phase, the only possibility for the observed cationization was a reaction in the gas phase. Due to the difficulty in completely removing the adventitious cations (Na(+) and K(+)) present in DHB and on sample surfaces, gas-phase cationization could not be demonstrated to be either the only or most important mechanism operating in the MALDI experiment.

Journal Article↗
PubMed1994

Divalent cation-dependent regulation of rat alveolar epithelial cell adhesion and spreading.

Interactions between cells and extracellular matrix are in large part mediated by integrins in divalent cation-dependent processes. Integrins are important for cell differentiation, proliferation, and migration during development and repair of diverse tissue types. The roles played by integrin adhesion receptors in the lung are just beginning to be investigated. It is plausible that integrins play a central role in mediating lung basement membrane influences on alveolar epithelial type II cell localization and differentiation. The current studies were carried out to determine the patterns of alveolar epithelial cell adherence and spreading on different substrata and their divalent cation and RGD requirements. We utilized a rat type II cell-derived cell line, LM5, and a human alveolar cell carcinoma cell line A549. Both cell types showed similar responses to divalent cations. Adhesion and spreading on different extracellular matrix components had different divalent cation requirements. Mn2+ enhanced adhesion and spreading on fibronectin (FN), type IV collagen, and laminin, but not on type I collagen or plastic. Mn(2+)-enhanced cell adhesion to FN was RGD-dependent and partially inhibited by an anti-alpha 5 integrin antibody. Small increases in Ca2+ concentration (0.1-0.5 mM), but not Mg2+, suppressed Mn(2+)-mediated adhesion and spreading. Thus, variations in the relative divalent cation concentrations in the vicinity of the integrin-ligand complex may modulate the receptor-acceptor interactions. These results support the view that alterations in extracellular divalent cations are important regulators of alveolar epithelial cell interactions with lung basement membrane.

Animals↗
PubMed1993

Renal epithelial cells show nonselective cation channel activity and express a gene related to the cGMP-gated photoreceptor channel.

Nonselective cation channels have been found in various parts of the nephron and represent a heterogeneous group of channels. We briefly review their putative physiological function. Renal epithelial nonselective cation channels may play a role in volume regulation, calcium entry, cell proliferation, and sodium reabsorption. In some renal epithelia cGMP seems to be involved in the regulation of nonselective cation channels. Furthermore, there is evidence that a gene related to the cGMP-gated photoreceptor channel, a well-characterized, nonselective cation channel, is also expressed in whole rat kidney tissue. In the context of these observations, we review recent findings from our own work on a nonselective cation channel in the M-1 mouse cortical collecting duct cell line. We could demonstrate that M-1 cells show nonselective cation channel activity in inside-out patches and express a gene related to the cGMP-gated photoreceptor channel (Proc. Natl. Acad. Sci. USA 89:10262-10266, 1992). The possibility of a relation between the kidney channel and the photoreceptor channel is discussed.

Adenosine Triphosphate↗
PubMed1994

Inositol-trisphosphate-dependent calcium currents precede cation currents in insect olfactory receptor neurons in vitro.

Specialized olfactory receptor neurons in insects respond to species-specific sex pheromones with transient rises in inositol trisphosphate and by opening pheromone-dependent cation channels. These channels resemble cation channels which are directly or indirectly Ca(2+)-dependent. But there appear to be no internal Ca2+ stores in the outer dendrite where the olfactory transduction cascade is thought to start. Hence, it remains to be determined whether an influx of external Ca2+ precedes pheromone-dependent cation currents. Patch clamp measurements in cultured olfactory receptor neurons from Manduca sexta reveal that a transient inward current precedes pheromone-dependent cation currents. A transient inositol trisphosphate-dependent Ca2+ current, also preceding cation currents with the characteristics of pheromone-dependent cation currents, shares properties with the transient pheromone-dependent current. These results match the biochemical measurements with the electrophysiological data obtained in insect olfactory receptor neurons.

Animals↗
PubMed1986

The cell surface of a restrictive fenestrated endothelium. II. Dynamics of cationic ferritin binding and the identification of heparin and heparan sulfate domains on the choriocapillaris.

The location and chemical composition of anionic sites on the endothelium of the choriocapillaris was investigated with cationic ferritin and enzyme digestion techniques. Cationic ferritin administered intravenously initially labeled essentially all fenestral diaphragms. Within 30 min after injection, no diaphragms remained labeled, but they could be relabeled by a second cationic ferritin injection. Following perfusion of cationic ferritin, the entire luminal front of the endothelium was labeled: the plasmalemma and fenestral, vesicle, and channel diaphragms. Perfusion of neuraminidase or chondroitinase did not affect subsequent cationic ferritin binding. In contrast, heparitinase removed anionic sites on all structures except fenestral diaphragms. Cationic ferritin did not mark the endothelium following heparinase digestion. All sites were cleaved with pronase E. These results indicate that heparin is the anionic moiety on fenestral diaphragms while the glycocalices of the plasmalemma and vesicle and channel diaphragms are rich in a heparan sulfate proteoglycan. Furthermore, since the heparan sulfate localized to these structures was digested by both heparinase and heparitinase, it is in a form similar to heparin. These findings demonstrate that the endothelium of the choriocapillaris bears cell-surface anionic components that are different than those described for fenestrated endothelia lining other vascular beds.

Animals↗
PubMed1992

Differential sensitivity of pneumolysin-induced channels to gating by divalent cations.

The induction of channels across planar lipid bilayers by purified, recombinant pneumolysin (a hemolytic protein from Streptococcus pneumoniae) has been studied by measuring increases in electrical conductivity. Pneumolysin-induced channels exhibit a wide range of single channel conductances (less than 50 pS to greater than 1 nS at 0.1 M KCl). Channels can be categorized on the basis of their K+:Cl- selectivity: the smallest channels are strongly cation selective, with t+ (the cation transference number) approaching 1.0; the largest channels are unselective (t+ approximately 0.5). Channels tend to remain open at all voltages (-150 to 150 mV); only the smallest channels exhibit any rectification. In the presence of divalent cations (1-5 mM Zn2+; 10-20 mM Ca2+), small (less than 50 pS) and medium-sized (50 pS to 1 nS) channels are closed in a voltage-dependent manner (more closure at higher voltages); at 0 voltage channels reopen. Overall selectivity is reduced by divalent cations, compatible with small, selective channels being closed preferentially to large, nonselective ones. It is concluded that a single molecular species (pneumolysin) induces multiple-sized channels that can be categorized by cation:anion selectivity and by their sensitivity to closure by divalent cations.

Bacterial Proteins↗
PubMed1994

Transport of K+ and other cations across phospholipid membranes by nonesterified fatty acids.

The rate of change of internal pH and transmembrane potential has been monitored in liposomes following the external addition of various cation salts. Oleic acid increases the transmembrane movement of H+ following the imposition of a K+ gradient. An initial fast change in internal pH is seen followed by a slower rate of alkalinization. High concentrations of the fatty acid enhance the rate comparable to that seen in the presence of nigericin in contrast to the effect of FCCP (carbonyl cyanide p-(tri-fluoromethoxy)phenyl hydrazone) which saturates at an intermediate value. The ability of nonesterified fatty acids to catalyze the movement of cations across the liposome membrane increases with the degree of unsaturation and decreases with increasing chain length. Li and Na salts cause a similar initial fast pH change but have less effect on the subsequent slower rate. Similarly, the main effect of divalent cation salts is on the initial fast change. The membrane potential can enhance or inhibit cation transport depending on its polarity with respect to the cation gradient. It is concluded that nonesterified fatty acids have the capability to complex with, and transport, a variety of cations across phospholipid bilayers. However, they do not act simply as proton/cation exchangers analogous to nigericin nor as protonophores analogous to FCCP. The full cycle of ionophoric action involves a combination of both functions.

Fatty Acids, Nonesterified↗
PubMed1994

Effects of metal cations on [3H]alpha,beta-methylene ATP binding in rat vas deferens.

In this study we have examined the effect of metal cations (as their chloride salts) on the binding of [3H]alpha,beta-methylene ATP ([3H]alpha beta meATP) to rat vas deferens membranes using a vacuum filtration receptor binding assay. Whereas NaCl and KCl (0.01 and 30 mM) did not affect total binding of 1 nM [3H]alpha beta meATP, several divalent and trivalent cation salts markedly increased binding. The trivalent cation salts, FeCl3 and AlCl3 (0.1 to 100 microM), produced the greatest increases in total binding of [3H]alpha beta meATP, however, their effects were most probably due to precipitation of the radioligand. In contrast, several divalent cations, at concentrations between 1 microM and 1-10 mM, increased total binding of [3H]alpha beta meATP to rat vas deferens by between 87% and 215% while having no effect on either filter binding or non specific binding. The following pEC50 values for potentiating binding of the radioligand were obtained: ZnCl2 (5.44), MnCl2 (4.52), CaCl2 (4.17), CoCl2 (4.06), MgCl2 (3.67) and BaCl2 (3.10). Both EDTA and EGTA (0.01-1 mM) inhibited the binding of the radioligand. The effects of ZnCl2, CaCl2 and MgCl2 were examined in saturation studies. In the absence of added divalent cations, [3H]alpha beta meATP labelled both high (pKd = 9.15) and low (pKd = 7.06) affinity binding sites. The affinity of the radioligand for its high affinity sites was increased by 3 mM CaCl2 (pKd = 9.56) and by 30 microM ZnCl2 (pKd = 9.46) but not by 3 mM MgCl2. The Bmax of the low affinity site for [3H]alpha beta meATP was increased (approximately 4 fold) by both 3 mM MgCl2 and 30 microM ZnCl2 but not by 3 mM CaCl2. The selective effect of CaCl2 on the high affinity binding sites enabled these sites to be labelled in the presence of 3 mM CaCl2 using a low concentration of [3H]alpha beta meATP (1 nM); the sites exhibited the binding characteristics expected of the P2x purinoceptor. The selective effect of MgCl2 on the low affinity binding sites enabled these sites to be labelled in the presence of 3 mM MgCl2 and using a high concentration of [3H]alpha beta meATP (100 nM). A comparison of the binding characteristics of the high and low affinity sites for [3H]alpha beta meATP revealed several other differences, in addition to their cation selectivity.(ABSTRACT TRUNCATED AT 400 WORDS)

Adenosine Triphosphate↗
PubMed1992

Activation of nonselective cation channels in the basolateral membrane of rat distal colon crypt cells by prostaglandin E2.

Ion channels in the basolateral membrane of colonic crypts were investigated with the patch-clamp technique during stimulation of secretion. Intact crypts were isolated from rat distal colon and the cell potential was recorded by addition of nystatin to the pipette solution. The cell resting potential in the base of the crypt was -74 +/- 1 mV (n = 90). Addition of 100 microM carbachol to the bath resulted in a transient hyperpolarization by 9 mV, which was probably due to the opening of basolateral K+ channels. In contrast, application of prostaglandin E2 (PGE2, 1 nM-1 microM) caused a dose-dependent depolarization in the base of the crypt. With 1 microM PGE2 cells depolarized from -74 +/- 1 to -27 +/- 2 mV (n = 26). Cell potential recordings in the midcrypt showed only a slight and transient depolarization after application of PGE2, whereas cells close to the surface of the crypt had no response. In the base of the crypt the PGE2-induced depolarization could be completely inhibited by addition of 50 microM flufenamic acid, a known blocker of nonselective cation channels. After substitution of all monovalent cations by N-methyl-D-glucamine in the bath, PGE2 had no significant effect on the cell potential. Cell-attached experiments with no nystatin in the patch pipette revealed the activation of ion channels in the basolateral membrane after application of PGE2. After excision of the membrane patch, these channels could be identified as nonselective cation channels. Experiments involving substitution of the bath solution showed that the channel is impermeable for Cl- and scarcely permeable for Ca2+ ions. The permeability sequence for monovalent cations, as calculated from reversal potentials, is NH4+ greater than Na+ = K+ greater than Rb+ = Li+ much greater than TRIS+ = NMDG+. Single channels are completely inhibited by flufenamic acid (50 microM), mefenamic acid (200 microM), as well as by 3',5-dichlorodiphenylamine-2-carboxylate. In conclusion, PGE2 activates nonselective cation channels in the basolateral membrane of cells in the base of colonic crypts. It is suggested that this mechanism initiates the secretion of K+ ions. Na+ influx through the nonselective cation channel will stimulate the Na+/K+ pump and active uptake of K+ at the basolateral side. K+ can leave the cell at the luminal side through K(+)-selective channels.

Animals↗
PubMed1992

Structural features of cation transport ATPases.

Several cation transport ATPases, sharing the common feature of a phosphorylated intermediate in the process of ATP utilization, are compared with respect to their subunit composition and amino acid sequence. The main component of these enzymes is a polypeptide chain of MW slightly exceeding 100,000, comprising an extramembranous globular head which is connected through a stalk to a membrane-bound region. With reference to the Ca2+ ATPase of sarcoplasmic reticulum, it is proposed that the catalytic (ATP binding and phosphorylation) domain resides in the extramembranous globular head, while cation binding occurs in the membrane region. Therefore, these two functional domains are separated by a distance of approximately 50 A. Alignment of amino acid sequences reveals extensive homology in the isoforms of the same ATPases, but relatively little homology in different cation ATPases. On the other hand, all cation ATPases considered in this analysis retain a consensus sequence of high homology, spanning the distance between the phosphorylation site and the preceding transmembrane helix. It is proposed that this sequence provides long-range functional linkage between catalytic and cation-binding domains. Thereby, translocation of bound cation occurs through a channel formed by transmembrane helices linked to the phosphorylation site. Additional sequences at the carboxyl terminal provide regulatory domains in certain ATPases.

Amino Acid Sequence↗
PubMed1976

The uptake and extrusion of monovalent cations by isolated heart mitochondria.

The factors involved in the movement of monovalent cations across the inner membrane of the isolate heart mitochondrion are reviewed. The evidence suggests that the energy-dependent uptake of K+ and Na+ which results in swelling of the matrix is an electrophoretic response to a negative internal potential. There are no clear cut indications that this electrophoretic cation movement is carrier-mediated and possible modes of entry which do not require a carrier are examined. The evidence also suggests that the monovalent cation for proton exchanger (Na+ greater than K+) present in the membrane may participate in the energy-dependent extrusion of accumulated ions. The two processes, electrophoreti c cation uptake (swelling) and exchange-dependent cation extrusion (contraction) may represent a means of controlling the volume of the mitochondrion within the functioning cell. A number of indications point to the possibility that the volume control process may be mediated by the divalent cations Ca+2 and Mg+2. Studies with mercurial reagents also implicate certain membrane thiol groups in the postulated volume control process.

Animals↗
PubMed1992

Tightly-bound divalent cation of actin.

Actin is known to undergo reversible monomer-polymer transitions that coincide with various cell activities such as cell shape changes, locomotion, endocytosis and exocytosis. This dynamic state of actin filament self-assembly and disassembly is thought to be regulated by the properties of the monomeric actin molecule and in vivo by the influence of actin-associated proteins. Of major importance to the properties of the monomeric actin molecule are the presence of one tightly-bound ATP and one tightly-bound divalent cation per molecule. In vivo the divalent cation is thought to be Mg2+ (Mg-actin) but in vitro standard purification procedures result in the preparation of Ca-actin. The affinity of actin for a divalent cation at the tight binding site is in the nanomolar range, much higher than earlier thought. The binding kinetics of Mg2+ and Ca2+ at the high affinity site on actin are considered in terms of a simple competitive binding mechanism. This model adequately describes the published observations regarding divalent cation exchange on actin. The effects of the tightly-bound cation, Mg2+ or Ca2+, on nucleotide binding and exchange on actin, actin ATP hydrolysis activity and nucleation and polymerization of actin are discussed. From the characteristics that are reviewed, it is apparent that the nature of the bound divalent cation has a significant effect on the properties of actin.

Actins↗