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PubMed2001

Binding citrate/DNA in presence of divalent cations. Potential mimicry of acidic peptides/DNA interactions.

Citric acid whose structure is comparable to that of small acidic peptides, can bind to DNA in the presence of divalent cations (Cu2+, Fe2+, Zn2+, Mg2+). Citrate-DNA interaction occurs also in a cell homogenate and in this experimental model too requires the presence of natural divalent cations. In fact the addition of 2 mM EDTA to cell homogenate strongly decreases the DNA-citrate binding. The results demonstrate that divalent cations can act as bridges between two acidic molecules and that citric acid can mimic the structure of acidic peptides.

Animals↗
PubMed1995

Suramin analogs, divalent cations and ATP gamma S as inhibitors of ecto-ATPase.

Ecto-nucleotidases are plasma membrane-bound enzymes that sequentially dephosphorylate extracellular nucleotides such as ATP. This breakdown of ATP and other nucleotides obscures the characterization and classification of P2 (nucleotide) receptors. We therefore studied suramin and several of its analogs, divalent cations and ATP gamma S for their ability to inhibit ecto-ATPase in human blood cells. Suramin itself and Ni2+ were the more potent, non-competitive inhibitors with micromolar affinity. ATP gamma S also displayed micromolar affinity and inhibited ecto-ATPase competitively. The data obtained with the divalent cations demonstrate that coordination of the phosphate chain but not the N7 of the adenine ring is required for the breakdown of ATP by ecto-ATPase. Divalent cations that coordinate both the phosphate chain and N7 inhibit ecto-ATPase in a non-competitive manner.

Adenosine Triphosphatases↗
PubMed1986

Divalent cation induced fusion and lipid lateral segregation in phosphatidylcholine-phosphatidic acid vesicles.

The interactions of unilamellar vesicles containing phosphatidylcholine (PC) and phosphatidic acid (PA) in the presence of calcium and magnesium were examined by fluorometric assays of vesicle lipid mixing, contents mixing, and contents leakage and by spray-freezing freeze-fracture electron microscopy. These results were correlated with calorimetric and fluorometric measurements of divalent cation induced lateral segregation of lipids in these vesicles under comparable conditions. PA-PC vesicles in the presence of calcium show a rapid but limited intermixing of vesicle lipids and contents, the extent of which increases as the vesicle size decreases or the PA content increases. Calcium produces massive aggregation and efficient mixing of the contents of vesicles containing high proportions of dioleoyl-PA or egg PA, but vesicle coalescence in the latter case is followed rapidly by vesicle collapse and massive leakage of contents. The effects of magnesium are similar for vesicles of very high PA content. However, in the presence of magnesium, vesicles containing lower amounts of PA exhibit "hemifusion", a mode of interaction in which vesicles aggregate and mix approximately 50% of their lipids, apparently representing the lipids of the outer monolayer of each vesicle, without significant mixing of vesicle contents or collapse of the vesicles. Fluorometric measurements of lipid lateral segregation demonstrate that lateral redistribution of lipids in PA-PC vesicles begins at submillimolar concentrations of divalent cations and shows no abrupt change at the "threshold" divalent cation concentration, above which coalescence of vesicles is observed. By correlating calorimetric and fluorometric measurements of lipid lateral segregation and mixing of vesicle components, we can demonstrate that lipid segregation is at least strongly correlated with calcium-promoted coalescence of PA-PC vesicles and is essential to the magnesium-promoted interactions of vesicles of low PA contents.

Cations, Divalent↗
PubMed1984

Anion and divalent cation activation of phosphoglycolate phosphatase from leaves.

Phosphoglycolate (P-glycolate) phosphatase was purified 223-fold from spinach leaves by (NH4)2SO4 fractionation, DEAE-cellulose chromatography, and Sephadex G-200 chromatography. The partially purified enzyme had a broad pH optimum between 5.6 and 8.0 and was specific for the hydrolysis of P-glycolate with a Km (P-glycolate) of 26 microM. The enzyme was activated by divalent cations including Mg2+, Co2+, Mn2+, and Zn2+, and by anions including Cl-, Br-, NO-3, and HCOO-. Neither anions nor divalent cations activated the enzyme without the other. The P-glycolate phosphatase activities from tobacco leaves or the green algae, Chlamydomonas reinhardtii, also required Mg2+ and were activated by chloride. In addition, the enzyme was allosterically inhibited by ribose 5-phosphate. The activation of P-glycolate phosphatase by both anions and divalent cations and the inhibition by ribose 5-phosphate may be involved in the in vivo regulation of P-glycolate phosphatase activity.

Anions↗
PubMed1987

Topographical relationships between the monovalent and divalent cation binding sites of des-1-41-light chain bovine plasma protein C and des-1-41-light chain-activated bovine plasma protein C.

The paramagnetic effect of Mn2+ on the longitudinal relaxation rate (T1)-1 of 205Tl+, when both cations are bound to des-1-41-light chain bovine plasma protein C (GDPC) and its activation product, des-1-41-light chain-activated bovine plasma protein C (GDAPC), has been assessed by 205Tl+ NMR spectroscopy. A substantial shortening of the T1 for Tl+ bound to either protein was observed in the presence of Mn2+, an effect not noted upon substitution of Mn2+ with the diamagnetic cation Ca2+, which is known to bind to these proteins in a similar fashion to Mn2+. This paramagnetic effect was employed to estimate distances between the monovalent and divalent cation sites in these proteins, approximately 6.7 +/- 0.2 A with GDPC and 8.3 +/- 0.2 A in GDAPC. These data suggest that a conformational alteration occurs upon activation of GDPC which leads to an increase in the distance between the monovalent and divalent cation sites.

Animals↗
PubMed1996

The catalytic domain of avian sarcoma virus integrase: conformation of the active-site residues in the presence of divalent cations.

BACKGROUND: Members of the structurally-related superfamily of enzymes that includes RNase H, RuvC resolvase, MuA transposase, and retroviral integrase require divalent cations for enzymatic activity. So far, cation positions are reported in the X-ray crystal structures of only two of these proteins, E. coli and human immunodeficiency virus 1 (HIV-1) RNase H. Details of the placement of metal ions in the active site of retroviral integrases are necessary for the understanding of the catalytic mechanism of these enzymes. RESULTS: The structure of the enzymatically active catalytic domain (residues 52-207) of avian sarcoma virus integrase (ASV IN) has been solved in the presence of divalent cations (Mn2+ or Mg2+), at 1.7-2.2 A resolution. A single ion of either type interacts with the carboxylate groups of the active site aspartates and uses four water molecules to complete its octahedral coordination. The placement of the aspartate side chains and metal ions is very similar to that observed in the RNase H members of this superfamily; however, the conformation of the catalytic aspartates in the active site of ASV IN differs significantly from that reported for the analogous residues in HIV-1 IN. CONCLUSIONS: Binding of the required metal ions does not lead to significant structural modifications in the active site of the catalytic domain of ASV IN. This indicates that at least one metal-binding site is preformed in the structure, and suggests that the observed constellation of the acidic residues represents a catalytically competent active site. Only a single divalent cation was observed even at extremely high concentrations of the metals. We conclude that either only one metal ion is needed for catalysis, or that a second metal-binding site can only exist in the presence of substrate and/or other domains of the protein. The unexpected differences between the active sites of ASV IN and HIV-1 IN remain unexplained; they may reflect the effects of crystal contacts on the active site of HIV-1 IN, or a tendency for structural polymorphism.

Avian Sarcoma Viruses↗
PubMed1998

Ligand binding results in divalent cation displacement from the alpha 2 beta 1 integrin I domain: evidence from terbium luminescence spectroscopy.

The alpha 2 beta 1 integrin serves as a cell surface collagen or collagen/laminin receptor. Binding of the integrin to its ligands is largely mediated by the alpha 2 subunit I domain and requires the presence of divalent cations. Terbium ion (Tb3+), a fluorescent trivalent cation that often binds divalent cation-binding sites on proteins, supported binding of the I domain to collagen with half-maximal binding occurring at 5.2 +/- 1.7 microM Tb3+. By fluorescence resonance energy transfer spectroscopy, Tb3+ showed specific and saturable binding to the recombinant I domain with a Kd of 27 +/- 4 microM. Although both Mg2+ and Mn2+ were capable of quenching Tb3+ fluorescence, Mn2+ was much more effective than Mg2+. The alpha 2 beta 1 integrin also binds the pro-alpha 1(I) collagen carboxyl-terminal propeptide in a Mg2+-dependent manner via the I domain. Recombinant propeptide was used to examine the effect of ligand on the Tb3+ binding properties of the alpha 2 integrin I domain. As propeptide bound to the I domain, Tb3+ fluorescence progressively diminished suggesting that as ligand binds to the I domain, either Tb3+ is displaced or its fluorescence is quenched. Consistent with the former possibility, little dissociation of collagen-bound I domain occurred upon the addition of EDTA and subsequent incubation. These data support a model in which (1) the divalent cation is required for initial ligand-binding activity of the I domain and (2) ligand binding results in subsequent metal ion displacement to generate a metal-free I domain-ligand complex.

Binding Sites↗
PubMed1998

The effect of extracellularly applied divalent cations on cytosolic Ca2+ in murine leydig cells: evidence for a Ca2+-sensing receptor.

1. The effect of extracellularly applied divalent cations upon cytosolic Ca2+ levels ([Ca2+]) was investigated in fura-2-loaded mouse Leydig (TM3) cells. 2. The extracellular application of Ca2+ (2.5-15 mM) or Ni2+ (0.5-5 mM) elicited concentration-dependent elevations in cytosolic [Ca2+] that were followed by decays to baseline levels. Extracellular Mg2+ (0.8-15 mM) failed to influence cytosolic [Ca2+]. 3. Conditioning applications of Ca2+ (2.5-10 mM), Mg2+ (2.5-15 mM) or Ni2+ (0.5-5 mM) all attenuated the cytosolic Ca2+ response to a subsequent test application of 5 mM [Ni2+]. 4. The amplitude of Ni2+-induced cytosolic Ca2+ signals remained constant in low-Ca2+ solutions. Such findings suggest a participation of Ca2+ release from intracellular stores. In parallel, depletion of Ca2+ stores by either ionomycin (5 microM, in low-Ca2+ solutions) or thapsigargin (4 microM) abolished or attenuated Ni2+-induced Ca2+ transients. 5. Ionomycin (5 microM) elevated cytosolic [Ca2+] in Ca2+-free solutions even after prior Ni2+ application, indicating the presence of Ni2+-insensitive stores. 6. Caffeine (250 and 500 microM) elevated cytosolic [Ca2+] and attenuated Ni2+-induced Ca2+ release. Furthermore, TM3 cells stained intensely with a specific anti-ryanodine receptor antiserum, Ab34. These findings suggest that Ca2+ release is regulated by ryanodine receptors. 7. Both membrane depolarization and hyperpolarization, brought about by changes in extracellular [K+] ([K+]e) in the presence of valinomycin (5 microM), altered the waveform of the Ni2+-induced cytosolic Ca2+ signal. Hyperpolarization, in addition, diminished the response magnitude. Such voltage-induced response modulation localizes the regulatory events to the Leydig cell plasma membrane. 8. We propose the existence of a cell surface divalent cation (Ca2+) receptor in Leydig cells, the activation of which triggers Ca2+ fluxes through ryanodine receptors.

Animals↗
PubMed1983

Self-assembly of simian virus 40 large T antigen oligomers by divalent cations.

In simian virus 40-transformed cells, simian virus 40 large T antigen can be detected in different forms separable by sucrose density gradient centrifugation. In our experiments, light forms sedimented around 5 to 7S, oligomers such as tetramers were detected around 16S, and higher aggregates sedimented in a broad distribution reaching above 23S. The oligomers sedimenting at and above 16S could be disassembled into the slowly sedimenting 5 to 7S forms by chelating agents [EDTA or ethylene bis(oxonitrilo)tetraacetate]. After the addition of divalent cations (CaCl2 or MgCl2) in excess of chelating agents, oligomeric forms reassembled and appeared in a sedimentation pattern resembling that observed before treatment with chelating agents. Time course studies permitted the identification of the 5 to 7S forms as precursors upon pulse-labeling (15 min); the 16S and higher oligomers were identified as the successors after a 14-h chase. Treatment of extracts of pulse-chase-labeled cells with chelating agents again disassembled the oligomers, whereas pulse-labeled precursors did not change their 5 to 7S sedimentation pattern. Adding an excess of divalent cations reassembled the pulse-chase-labeled T antigen to oligomers but did not influence the sedimentation behavior of pulse-labeled 5 to 7S precursors. It is therefore reasonable to assume that a posttranslational modulation induces divalent cation binding, leading finally to the oligomerization of T antigen. Thus, some of the multifunctional activities of T antigen can be dictated by divalent cation binding properties.

Antigens, Viral↗
PubMed1989

High affinity divalent cation binding to actin. Effect of low affinity salt binding.

Monomeric actin labeled with the fluorescent probe N-iodoacetyl-N'-(5-sulfo-1-naphthyl)ethylenediamine (1,5-I-AEDANS-actin) displays a fast fluorescence intensity increase immediately upon addition of salt and then a slow fluorescence intensity change concurrent with Ca2+/Mg2+ exchange at the high affinity divalent cation binding site on actin. The fast change appears to reflect competitive binding of K+ at low affinity (nonspecific) sites and of Mg2+ or Ca2+ at low and intermediate affinity sites. Binding of cation at the low affinity sites (but apparently not at the intermediate affinity sites) results in an increase in k-Ca and k-Mg and thus a decrease in affinity for divalent cations at the high affinity site. The effect of Mg2+ on k-Ca is twice that of K+ for equal fractional saturations of the low affinity binding, and the effect of K+ and Mg2+ together on k-Ca reflects competitive binding at the low affinity sites. Thus the affinity and kinetics of divalent cation binding at the high affinity site of actin are significantly affected by concurrent cation binding at low affinity sites.

Actins↗
PubMed2002

Binding symmetry of extracellular divalent cations to conduction pore studied using tandem dimers of a CNG channel.

Cyclic nucleotide-gated (CNG) channels are composed of the tetramer of alpha-subunit alone or alpha- and beta-subunits. The alpha-subunits of these channels have a conserved glutamate (Glu) residue within the pore-forming region and the residue determines the selectivity as well as the affinity for the extracellular divalent cations. Using the high-affinity mutant (E363D) of bovine retinal CNG channel in which the Glu at position 363 was replaced to Asp, we constructed tandem dimers and investigated the binding characteristics of divalent cations to the site. The gating and permeation characteristics of individual homomeric tandem dimers are indistinguishable to those of homo-tetramers formed by parental monomers. The heteromeric tandem dimers showed the binding affinity for Sr(2+) identical to the geometric mean of the affinities for two parent channels, indicating the energy additive and thus the simultaneous interaction. On the other hand, the binding affinity for Mg(2+) followed the harmonic mean of those parent channels indicating that Mg(2+) interacts more strongly with the subunit bearing Asp residue at the position. Thus the results strongly suggest that the Glu363 residues in the CNG channel pore be flexible enough to adapt different binding symmetries for different divalent cations. Moreover, the simultaneous interaction between the four Glu residues and Sr(2+) provides an important structural constraint to the CNG channel outer vestibule of unknown structure.

Amino Acid Sequence↗
PubMed1991

Activation and inhibition of the brush-border membrane-bound alkaline phosphatase activity of Hymenolepis diminuta (Cestoda) by divalent cations.

In the absence of exogenous divalent cations, the isolated brush-border plasma membrane of Hymenolepsis diminuta possesses alkaline phosphatase activity (APA). APA is stimulated in the presence of exogenous Mg2+ and inhibited by low concentrations of Zn2+ or high concentrations of Ca2+, and inhibition of APA by Zn2+ is reversed by both Mg2+ and Ca2+. APA is inhibited by ethylenediamine tetraacetic acid (EDTA), ethyleneglycol-bis-(beta-aminoethyl ether) N,N'-tetraacetic acid, and 1,10-phenanthroline in time- and concentration-dependent fashions, with EDTA being the most effective inhibitor. Following treatment with EDTA, APA is restored by Mg2+ and, to a lesser extent, by Ca2+, but not by Zn2+. Thus, APA represents a Mg2(+)-dependent enzyme that can be partly activated by Ca2+ but only in the absence of Mg2+.

Alkaline Phosphatase↗
PubMed1977

HCO(3) Influx Across the Plasmalemma of Chara corallina: Divalent Cation Requirement.

An absolute requirement for divalent cations is reported for H(14)CO(3) (-) influx in Chara corallina. Effective substitution of eluted Ca(2+) by Mg(2+) and Sr(2+) was observed, but Mn(2+) was completely ineffective in restoring H(14)CO(3) (-) transport activity. Similarly, La(3+) could not substitute for Ca(2+) in this system. Low concentrations of ethylenediaminetetraacetate (0.01 to 0.06 mm) significantly enhanced the rate at which H(14)CO(3) (-) transport capacity was lost.Examination of the response of OH(-) efflux, during Ca(2+)-free treatment, indicated that the cellular control over OH(-) efflux remained unaffected until membrane integrity became severely affected. This conclusion was supported by the response of OH(-) efflux to 10 mm K(+). Therefore, assimilation of H(14)CO(3) (-) is not rate-limited by an effect of Ca(2+) elution on the OH(-) transport system. Kinetic experiments indicated that Ca(2+) removal from the membrane resulted in noncompetitive inhibition of H(14)CO(3) (-) assimilation; the apparent Michaelis constant remained unaltered over a wide range of conditions. An hypothesis is presented which suggests that membrane integrity is necessary for HCO(3) (-) transport to occur, but Ca(2+) (Mg(2+), Sr(2+)), per se, must be bound to the transport complex before activity is established.

Journal Article↗
PubMed1981

Mechanisms of cation permeation across apical cell membrane of Necturus gallbladder: effects of luminal pH and divalent cations on K+ and Na+ permeability.

Conventional microelectrode techniques were combined with unilateral mucosal ionic substitutions to determine the effects of luminal pH and luminal alkali-earth cation concentrations on apical membrane cation permeability in Necturus gallbladder epithelium. Acidification of the mucosal solution caused reversible depolarization of both cell membranes and increase of transepithelial resistance. Low pH media also caused: (a) reduction of the apical membrane depolarization induced by high K, and (b) increase of the apical membrane hyperpolarization produced by Na replacement with Li or N-Methyl-D-glucamine. These results, in conjunction with estimates of cell membrane conductances, indicate that acidification of the luminal solution produces a reduction of apical membrane K permeability (PK). Addition of alkali earth cations (Mg2+, Ca2+, Sr2+, or Ba2+) produced cell membrane depolarization, increase of relative resistance of the luminal membrane and reduction of the apical membrane potential change produced by a high-K mucosal medium. These results, as those produced by low pH, can be explained by a reduction of apical membrane PK. The effects of Ba2+ on membrane potential and relative apical membrane PK were larger than those of all other four cations at all concentrations tested (1-10 mM). The effect of Sr2+ was significantly larger than those of Mg2+ and Ca2+ at 10 mM, but not different at 5 mM. The reduction of PK produced by mucosal acidification appears to be mediated by: (a) nonspecific titration of membrane fixed negative charges, and (b) an effect of luminal proton activity on the apical K channel. Divalent cations reduce apical membrane PK probably by screening negative surface charges. The larger magnitude of the effects of Ba2+ and Sr2+ can be explained by binding to membrane sites, in the surface or in the K channel, in addition to their screening effect. We suggest that the action of luminal pH on K secretion in some segments of the renal tubule could be mediated in part by this pH-dependent K permeability of the luminal membrane.

Animals↗
PubMed1980

Divalent cations as charge carriers during two functionally different membrane currents in the ciliate Stylonychia.

We have investigated the ability of various divalent cations to carry current through membrane channels in ciliates activated by mechanical stimulation and by membrane depolarization. Both types of channels are identified as Ca2+ channels. Whereas Ba2+ ions and Sr2+ ions can replace Ca2+ ions as charge carriers during either kind of current, Mg2+ ions can carry the current evoked by mechanical stimulation but not the current elicited by membrane depolarization. Mn2+ ions did not carry either of these currents, and they reduced the currents carried by Ca2+ ions. Our experiments suggest that the mechano-sensitive and the voltage-sensitive channels exhibit different selectivities for divalent cations.

Animals↗
PubMed1994

Effects of divalent cations on adenosine agonist binding to A1 receptors and non-A1/non-A2 sites in rat cerebral cortex.

In the present study results are reported concerning the effects of several divalent cations on the binding characteristics of [3H]-cyclohexyladenosine on A1 adenosine receptors and of [3H]-N-ethylcarboxamidoadenosine on non-A1/non-A2 sites in membranes from cerebral cortex of the rat. The [3H]-cyclohexyladenosine binding to A1 receptors was dose-dependently increased by Mn2+, Co2+, Ca2+. The binding characteristics of the agonist were differently affected by Ca2+/Mn2+ and Mg2+. Ca2+ and Mn2+ increased the Bmax value without any change in Kd, whereas Mg2+ decreased the Kd value without changing the Bmax. In the presence of Ca2+ and Mg2+ the Kd value was similar to that obtained in the presence of Mg2+, whereas the Bmax value was similar to the apparent number of binding sites calculated in the presence of Ca2+. The cations, Cu2+, Cd2+, Zn2+, decreased the A1 binding with IC50 values of 19.6 microM, 39.2 microM and 103.9 microM, respectively. The binding characteristics of [3H]-N-ethylcarboxamidoadenosine to non-A1/non-A2 sites were affected by Ca2+, Mn2+, Co2+ and Mg2+ in the opposite manner to A1 receptors. They decreased the binding with IC50 values of 20.1 mM, 22.8 mM, 93.0 mM and 18.1 mM, respectively. This occurs through an enhancement in Kd values without changes in the number of binding sites. The findings on A1 receptor and non-A1/non-A2 binding site, taken together, suggest that cations could also exert a modulatory action via specific interactions with divalent cation binding sites on the receptor molecule.

Adenosine↗
PubMed2004

Magnesium-inhibited, TRPM6/7-like channel in cardiac myocytes: permeation of divalent cations and pH-mediated regulation.

Cardiac tissue expresses several TRP proteins as well as a Mg2+ -inhibited, non-selective cation current (IMIC) that bears many characteristics of TRP channel currents. We used the whole-cell voltage clamp technique in pig and rat ventricular myocytes to characterize the permeation, blockage properties and regulation of the cardiac IMIC channels in order to compare them with TRP channels, in particular with Mg2+ -sensitive TRPM6 and TRPM7. We show that removing extracellular divalent cations unmasks large inward and outward monovalent currents, which can be inhibited by intracellular Mg2+. Inward currents are suppressed upon replacing extracellular Na+ by NMDG+. Divalent cations block monovalent IMIC and, at 10-20 mm, carry measurable currents. Their efficacy sequence in decreasing outward IMIC (Ni2+ = Mg2+ > Ca2+ > Ba2+) and in inducing inward IMIC (Ni2+ >> Mg2+ = Ca2+ approximately Ba2+), and their permeabilities calculated from reversal potentials are similar to those of TRPM6 and TRPM7 channels. The trivalent cations Gd3+ and Dy3+ also block IMIC in a voltage-dependent manner (delta = 0.4-0.5). In addition they inhibit the inward current carried by divalent cations. IMIC is regulated by pH. Decreasing or increasing extracellular pH decreased and increased IMIC, respectively (pH0.5 = 6.9, nH = 0.98). Qualitatively similar results were obtained on IMIC in rat basophilic leukaemia cells. These effects in cardiac myocytes were absent in the presence of high intracellular buffering by 40 mm Hepes. Our results suggest that IMIC in cardiac cells is due to TRPM channels, most probably to TRPM6 or TRPM7 channels or to their heteromultimeres.

Animals↗
PubMed1978

The effects of divalent cations on the rotational mobility of myosin, heavy meromyosin and myosin subfragment-1 and on the binding of heavy meromyosin to actin.

The effects of the divalent cations Mg2+, Mn2+ and Ca2+ on the Brownian rotational motion of fluorescently labeled myosin, heavy meromyosin and myosin subfragment-1 were measured by the method of time-resolved fluorescence depolarization. When Mg2+ was added to solutions of myosin or heavy meromyosin and EDTA, their rotational mobility increased. Ca2+ had no effect. Mn2+ increased the mobility of heavy meromyosin but decreased that of myosin. None of these divalent cations effected the mobility of subfragment-1. The binding of heavy meromyosin to actin was affected very little by Mg2+ or EDTA over a wide range of conditions. Divalent cations appear to change the swivel about which the heads of myosin rotate, presumably by binding to light chain 2 (also called DTNB light chain). However, the heads are still able to bind actin in nearly the same way whether Mg2+ is present or not. The concentration of free Mg2+ for the mid-point of the change in heavy meromyosin mobility is in good agreement with that for EDTA activation of ATPase activity. This suggests that EDTA activation is due to removal of Mg2+ bound to myosin itself.

Actins↗