Mechanism of energization of uptake of the fluorescent dye 2-(4-dimethylaminostyryl)-1-ethylpyridinium cation [DMP+] into an acrA strain of Escherichia coli.

The mechanism of uptake of the fluorescent dye 2-(4-dimethylaminostyryl)-1-ethylpyridinium cation (DMP+) into cells and vesicles of the acrA strain AS-1 of Escherichia coli was examined. Uptake was energized by substrate oxidation and discharged by uncouplers. Uptake was enhanced by the presence of tetraphenylphosphonium cation, tetraphenylboron anion and tributyltin chloride, which may inhibit the efflux system for DMP+. Uptake was inhibited by 5-methoxyindole-2-carboxylic acid (MIC). By the use of ionophores with right-side-out vesicles loaded with monovalent cations it was shown that DMP+ uptake could be driven both by the establishment of a membrane potential across the vesicle membrane and by a H+/DMP+ antiport system. Attempts to demonstrate the latter mechanism in everted membrane vesicles were unsuccessful.     

The concentration dependence of the depolarization of yeast by monovalent cations.

Monovalent cations decrease the initial rate of uptake of the membrane potential probe 2-(dimethylaminostyryl)-1-ethyl-pyridinium (DMP) into metabolizing cells, showing that the cells are depolarized. A steep decrease in this rate was found even at low cation concentrations, reaching 62%, 42%, 58%, 40% and 40% at high concentrations of K+, Rb+, Cs+, Na+ and Li+, respectively. The corresponding concentrations at which half-maximum decrease was found were 0.22, 0.36, 1.2, 17 and 17 mM. These values are of the same order of magnitude as the half-saturation concentrations for monovalent cation uptake by the yeast.     

Interaction of phosphate with monovalent cation uptake in yeast.

The uptake of monovalent cations by yeast via the monovalent cation uptake mechanism is inhibited by phosphate. The inhibition of Rb+ uptake shows saturation kinetics and the phosphate concentration at which half-maximal inhibition is observed is equal to the Km of phosphate for the sodium-independent phosphate uptake mechanism. The kinetic coefficients of Rb+ and TI+ uptake are affected by phosphate: the maximal rate of uptake is decreased and the apparent affinity constants for the translocation sites are increased. In the case of Na+ uptake, the inhibition by phosphate may be partly or completely compensated by stimulation of Na+ uptake via a sodium-phosphate cotransport mechanism. Phosphate effects a transient stimulation of the efflux of the lipophilic cation dibenzyldimethylammonium from preloaded yeast cells and a transient inhibition of dibenzyldimethylammonium uptake. Possibly, the inhibition of monovalent cation uptake in yeast can be explained by a transient depolarization of the cell membrane by phosphate.     

Kinetics of Ca2+ and Sr2+ uptake by yeast. Effects of pH, cations and phosphate.

The uptake of Ca2+ and Sr2+ by the yeast Saccharomyces cerevisiae is energy dependent, and shows a deviation from simple Michaelis-Menten kinetics. A model is discussed that takes into account the effect of the surface potential and the membrane potential on uptake kinetics. The rate of Ca2+ and Sr2+ uptake is influenced by the cell pH and by the medium pH. The inhibition of uptake at low concentration of Ca2+ and Sr2+ at low pH may be explained by a decrease of the surface potential. The inhibition of Ca2+ and Sr2+ uptake by monovalent cations is independent of the divalent cation concentration. The inhibition shows saturation kinetics, and the concentration of monovalent cation at which half-maximal inhibition is observed, is equal to the affinity constant of this ion for the monovalent cation transport system. The inhibition of divalent cation uptake by monovalent cations appears to be related to depolarization of the cell membrane. Phosphate exerts a dual effect on uptake of divalent cations: and initial inhibition and a secondary stimulation. The inhibition shows saturation kinetics, and the inhibition constant is equal to the affinity constant of phosphate for its transport mechanism. The secondary stimulation can only partly be explained by a decrease of the cell pH, suggesting interaction of intracellular phosphate, or a phosphorylated compound, with the translocation mechanism.     

Some characteristics of the uptake of glutamine by corn scutellum

Slices of corn scutellum were used to study amino acid uptake, a natural function of this tissue. The uptake of glutamine was found to be inhibited by several monovalent cations. The accompanying anion did not affect the inhibition. Divalent cations stimulated glutamine uptake, particularly at high glutamine concentrations. The inhibition by monovalent cations was reversed by divalent cations.     

Inhibition of the rat blood–brain barrier choline transporter by manganese chloride

Choline transport has been characterized by multiple mechanisms including the blood-brain barrier (BBB), and high- and low-affinity systems. Each mechanism has unique locations and characteristics yet retain some similarities. Previous studies have demonstrated cationic competition by monovalent cations at the BBB and cation divalent manganese in the high-affinity system. To evaluate the effects of divalent manganese inhibition as well as other cationic metals at the BBB choline transporter, brain choline uptake was evaluated in the presence of certain metals of interest in Fischer-344 rats using the in situ brain perfusion technique. Brain choline uptake was inhibited in the presence of Cd(2+) (73 +/- 2%) and Mn(2+) (44 +/- 6%), whereas no inhibition was observed with Cu(2+) and Al(3+). Furthermore, it was found that manganese caused a reduction in brain choline uptake and significant regional choline uptake inhibition in the frontal and parietal cortex, the hippocampus and the caudate putamen (45 +/- 3%, 68 +/- 18%, 58 +/- 9% and 46 +/- 15%, respectively). These results suggest that choline uptake into the CNS can be inhibited by divalent cationic metals and monovalent cations. In addition, the choline transporter may be a means by which manganese enters the brain.     

Interaction of phosphate with monovalent cation uptake in yeast

The uptake of monovalent cations by yeast via the monovalent cation uptake mechanism is inhibited by phosphate. The inhibition of Rb⁺ uptake shows saturation kinetics and the phosphate concentration at which halfmaximal inhibition is observed is equal to the K_m of phosphate for the sodiumindependent phosphate uptake mechanism. The kinetic coefficients of Rb⁺ and Tl⁺ uptake are affected by phosphate: the maximal rate of uptake is decreased and the apparent affinity constants for the translocation sites are increased.In the case of Na⁺ uptake, the inhibition by phosphate may be partly or completely compensated by stimulation of Na⁺ uptake via a sodium-phosphate cotransport mechanism.Phosphate effects a transient stimulation of the efflux of the lipophilic cation dibenzyldimenthylammonium from preloaded yeast cells and a transient inhibition of dibenzyldimethylammonium eptake. Possibly, the inhibition of monovalent cation uptake in yeast can be explained by a transient depolarization of the cell membrane by phosphate.     

Kinetics of Ca2+ and Sr2+ uptake by yeast. Effects of pH,cations and phosphate

The uptake of Ca²⁺ and Sr²⁺ by the yeast Saccharomyces cerevisiae is energy dependent, and shows a deviation from simple Michaelis-Menten kinetics. A model is discussed that takes into account the effect of the surface potential and the membrane potential on uptake kinetics.The rate of Ca²⁺ and Sr²⁺ uptake is influenced by the cell pH and by the medium pH. The inhibition of uptake at low concentrations of Ca²⁺ and Sr²⁺ at low pH may be explained by a decrease of the surface potential.The inhibition of Ca²⁺ and Sr²⁺ uptake by monovalent cations is independent of the divalent cation concentration. The inhibition shows saturation kinetics, and the concentration of monovalent cation at which half-maximal inhibition is observed, is equal to the affinity constant of this ion for the monovalent cation transport system. The inhibition of divalent cation uptake by monovalent cations appears to be related to depolarization of the cell membrane.Phosphate exerts a dual effect on uptake of divalent cations: and initial inhibition and a secondary stimulation. The inhibition shows saturation kinetics, and the inhibition constant is equal to the affinity constant of phosphate for its transport mechanism. The secondary stimulation can only partly be explained by a decrease of the cell pH, suggesting interaction of intracellular phosphate, or a phosphorylated compound, with the translocation mechanism.     

Kinetics of ion translocation across charged membranes mediated by a two-site transport mechanism. Effects of polyvalent cations upon rubidium uptake into yeast cells.

(1) The effect of surface charge upon the kinetics of monovalent cation translocation via a two-site mechanism is investigated theroretically. (2) According to the model dealt with, typical relations are expected for the dependence of the kinetic parameters of the translocation process upon the concentration of a polyvalent cation, differing essentially from those derived for the case in which the membrane carries no excess charge. (3) Even when a polyvalent cation does not compete with the substrate cation for binding to the translocation sites, apparently competitive inhibition may occur when the membrane is negatively charged. (4) The model is tested experimentally by studying the effects of the polyvalent cations Mg2+, Sr2+, Ca2+, Ba2+ and Al3+ upon Rb+ uptake into yeast cells at pH 4.5 A good applicability is found. (5) Equimolar concentrations of polyvalent cations reduce the rate of the Rb+ uptake into yeast cells in the order Mg2+ less than Sr2+ less than Ca2+ less than Ba2+ less than Al3+. (6) The conclusion is reached that the reduction in the rate of Rb+ uptake caused by the polyvalent cations applied results mainly from screening of the negative fixed charges on the membrane surface and binding to these negative sites rather than competition with Rb+ for the transport sites. (7) The results of our investigation indicate the affinity of the alkaline-earth cations for the negative fixed charges on the surface to the yeast cell membrane increases in the orther Mg2+ less than Sr2 less than Ca2+ less than Ba2+. (8) Probably mainly phosphoryl groups determine the net charge on the membrane of the yeast cell at a medium pH of 4.5.     

Co-transport of anions and neutral solutes with cations across charged biological membranes. Effects of surrface potential on uptake kinetics

General rate equations have been developed for the co-transport of an anion with one or two cations across a negatively charged biological membrane. The effects of surface potential on the kinetical parameters of co-transport of monovalent anions with monovalent cations have been investigated in more detail. The influence of changes in the surface potential on ion uptake kinetics appears to be markedly affected by the properties of the co-transport system. This can be shown by investigating boundary cases of the general model, namely (a) random order of binding of the ions, (b) anion binds before cations, (c) cations bind before anion. Since the effects of the surface potential are different for these three cases, these effects might serve as (additional) discrimination criteria.The effect of the surface potential on anion uptake kinetics via a co-transport system to which two cations can bind is rather complex: maxima or minima of the apparent affinity constant K_m of anion uptake may occur. Not only the magnitude of the effect of changes in the surface potential, but also its direction (stimulation, inhibition), is influenced by the co-substrate (cation) concentration. Such effects may also occur if only one cation can bind to the translocator, provided that OH^? ions compete for the anion transport site.In addition, the case of co-transport of a neutral solute with a monovalent cation has been investigated. It has been shown, that monovalent cation has been investigated. It has been shown, that also in this case, the effect of changes in the surfaces potential is affected by the order of binding of the substrates to the translocator.     

The role of glutamic acid-69 in the activation of Citrobacter freundii tyrosine phenol-lyase by monovalent cations

Tyrosine phenol-lyase (TPL) from Citrobacter freundii is activated about 30-fold by monovalent cations, the most effective being K(+), NH(4)(+), and Rb(+). Previous X-ray crystal structure analysis has demonstrated that the monovalent cation binding site is located at the interface between subunits, with ligands contributed by the carbonyl oxygens of Gly52 and Asn262 from one chain and monodentate ligation by one of the epsilon-oxygens of Glu69 from another chain [Antson, A. A., Demidkina, T. V., Gollnick, P., Dauter, Z., Von Tersch, R. L., Long, J., Berezhnoy, S. N., Phillips, R. S., Harutyunyan, E. H., and Wilson, K. S. (1993) Biochemistry 32, 4195]. We have studied the effect of mutation of Glu69 to glutamine (E69Q) and aspartate (E69D) to determine the role of Glu69 in the activation of TPL. E69Q TPL is activated by K(+), NH(4)(+), and Rb(+), with K(D) values similar to wild-type TPL, indicating that the negative charge on Glu69 is not necessary for cation binding and activation. In contrast, E69D TPL exhibits very low basal activity and only weak activation by monovalent cations, even though monovalent cations are capable of binding, indicating that the geometry of the monovalent cation binding site is critical for activation. Rapid-scanning stopped-flow kinetic studies of wild-type TPL show that the activating effect of the cation is seen in an acceleration of rates of quinonoid intermediate formation (30-50-fold) and of phenol elimination. Similar rapid-scanning stopped-flow results were obtained with E69Q TPL; however, E69D TPL shows only a 4-fold increase in the rate of quinonoid intermediate formation with K(+). Preincubation of TPL with monovalent cations is necessary to observe the rate acceleration in stopped flow kinetic experiments, suggesting that the activation of TPL by monovalent cations is a slow process. In agreement with this conclusion, a slow increase (k < 0.5 s(-)(1)) in fluorescence intensity (lambda(ex) = 420 nm, lambda(em) = 505 nm) is observed when wild-type and E69Q TPL are mixed with K(+), Rb(+), and NH(4)(+) but not Li(+) or Na(+). E69D TPL shows no change in fluorescence under these conditions. High concentrations (>100 mM) of all monovalent cations result in inhibition of wild-type TPL. This inhibition is probably due to cation binding to the ES complex to form a complex that releases pyruvate slowly.     

Uridine uptake inhibition in Novikoff hepatoma cells by perturbants of intracellular Ca2+ and K+ levels

The rate of uptake of uridine into the acid-soluble fraction of Novikoff hepatoma cells is inhibited by low concentrations of the ionophores A23187 and gramicidin and other perturbants of intracellular cation levels. Inhibition of uridine uptake by A23187 is dependent on Ca2+ and is reduced by serum and high levels of Mg2+. The effectiveness of A23187 is dependent on the Ca2+/Mg2+ ratio rather than the absolute concentration of either ion. Inhibition of uridine uptake by gramicidin is not significantly affected by serum or divalent cations. Other effectors of monovalent cation flux such as ouabain and valinomycin also inhibit uridine uptake. These results indicate that net uptake of uridine may be influenced by intracellular levels of certain monovalent and divalent inorganic cations.     

Sodium and rubidium uptake in cells transformed by Rous sarcoma virus

Rates of uptake and intracellular concentrations of monovalent cations were measured in virus-transformed and nontransformed chick embryo (CE) cells. Uptake of 22Na+ into cells transformed by the BH strain of Rous sarcoma virus (RSV-BH) (CE-BH) was about double the rate of uptake into CE cells, or cells transformed by the Schmidt-Ruppin strain (RSV-SR): CE-SR. Likewise, the rate of efflux of 22Na+ was greater in CE-BH cells than in CE or CE-SR cells. The greater permeability of CE-BH cells to Na+ was apparent in higher intracellular Na+ concentrations. Experiments with cells exhibiting temperature-dependent transformation showed that new RNA and protein synthesis was a requirement for the acquisition of increased Na+ permeability, suggesting that the change is an indirect effect of the virus-coded transformation-inducing protein. Rates of 86Rb+ uptake, used as a measure of K+ influx, were indistinguishable in CE, CE-BH, and CE-SR cells. Also, equilibrium intracellular levels of 86Rb+ were similar in transformed and nontransformed cells, as were observed concentrations of K+. Also, no differences in ATPase activity, as indicated by ouabain binding or temperature sensitivity, were observed. We conclude that monovalent cations play no direct role in RSV-induced transformation, although the higher levels of Na+ in CE-BH cells may be responsible for other distinguishing biochemical features of these cells.     

The effect of monovalent cations on calcium efflux in yeasts

The properties of the calcium efflux system in the yeast Saccharomyces cerevisiae were investigated. After growing the cells overnight in medium containing ⁴⁵Ca, the cells were transferred to medium containing glucose, Hepes buffer (pH 5.2) and monovalent cations. The presence of potassium or sodium in the medium induced efflux of calcium from the cells. The magnitude of the efflux was dependent on the concentration of these cations in the medium. The time course of calcium efflux was analyzed, and two types of exchangeable calcium pools, which turned over at different rates, were detected: ‘Fast turnover’ and ‘slow turnover’. Increase in the concentration of monovalent cations in the medium caused an increase in the fraction of cellular calcium which turned over at a fast rate, and activation of calcium efflux from the ‘slow turnover’ calcium pool. The specific changes in the parameters of calcium efflux induced by monovalent cations were different from those reported previously to be induced by divalent cations. Both processes, i.e. activation of calcium efflux by monovalent and by divalent cations, were found to be additive, indicating that they operate via different mechanisms. Experiments using the respiratory inhibitor Antimycin A, showed that stimulation of calcium efflux by monovalent cations is energy dependent. Lanthanum ions which are known to inhibit calcium influx into yeast cells, inhibitted the activation of calcium efflux by both divalent and monovalent cations. Determination of the cationic composition of the cells indicated that the stimulation of calcium efflux was accompanied by influx of potassium or sodium into the cells.     

Inhibitory analysis of the monovalent metals' cations interaction with the system of Na+-dependent Ca2+ efflux from the liver mitochondria

Kinetic analysis reveals the mainly competitive inhibition of Na+-dependent Ca2+ efflux from mitochondria by cations of monovalent metals. Potency of the inhibitory effect of metals' cations on Na+-dependent Ca2+ efflux from mitochondria matrix increases in such an order (I50, mM): Cs+ (137.11) < Rb+ (122.63) < Li+ (24.59) < Tl+ (0.541). The results of correlation analysis show that sodium ions translocation by mitochondrial exchanger and its inhibition by the cations of monovalent metals is determined by their affinity for the oxygen-containing ligands and are accompanied with the ions dehydration. Inhibition of the mitochondrial Na+/Ca2+ exchanger by monovalent metal cations is also accompanied with the inhibition of cooperative interactions of metal ions with the ionbinding centers during transport cycle, which can be one of the mechanisms of the inhibition of ions translocation by this ion-transporting system.     

Inhibition of adenylate cyclase from luteinized rat ovary by monovalent cations: roles of the stimulatory guanine nucleotide-binding regulatory component and stimulatory hormone receptor

Sodium and other monovalent cations (added as chloride salts) inhibited adenylate cyclase of luteinized rat ovary. Sodium chloride (150 mM) inhibited basal enzyme activity by 20%. Sodium chloride inhibition was enhanced to 34-54% under conditions of enzyme stimulation by guanine nucleotides (GTP and its nonhydrolyzable analog 5'-guanylyl imidodiphosphate), fluoride anion, and agonists (ovine luteinizing hormone (oLH) and the beta-adrenergic catecholamine isoproterenol) acting at stimulatory receptors linked to adenylate cyclase. Sodium chloride inhibition was dependent on salt concentration over a wide range (25-800 mM) as well as the concentrations of GTP and oLH. Inhibition by NaCl was of rapid onset and appeared to be reversible. The order of inhibitory potency of monovalent cations was Li+ greater than Na+ greater than K+. The role of individual components of adenylate cyclase in the inhibitory action of monovalent cations was examined. Exotoxins of Vibrio cholerae and Bordetella pertussis were used to determine respectively the involvement of the stimulatory and inhibitory guanine nucleotide-binding regulatory components (Ns and Ni) in NaCl inhibition. Sodium chloride inhibited cholera toxin-activated adenylate cyclase activity by 29%. Ni did not appear to mediate cation inhibition of adenylate cyclase because pertussis toxin did not attenuate inhibition by NaCl. Enzyme stimulation by agents (forskolin and Mn2+) thought to activate the catalytic component directly was not inhibited by NaCl but was instead significantly enhanced. Sodium chloride (150 mM) increased both the Kd for high-affinity binding of oLH to 125I-human chorionic gonadotropin binding sites and the Kact for oLH stimulation of adenylate cyclase by sevenfold. In contrast, NaCl had no appreciable effect on either isoproterenol binding to (-)-[125I]iodopindolol binding sites or the Kact for isoproterenol stimulation of adenylate cyclase. The results suggest that in luteinized rat ovary monovalent cations uncouple, or dissociate, Ns from the catalytic component and, in a distinct action, reduce gonadotropin receptor affinity for hormone. Dissociation of the inhibitory influence of Ni from direct catalytic activation could account for NaCl enhancement of forskolin- and Mn2+-associated activities. On the basis of these results, the spectrum of divergent stimulatory and inhibitory effects of monovalent cations on adenylate cyclase activities in a variety of tissues may be interpreted in terms of differential enzyme susceptibilities to cation-induced uncoupling of N and catalytic component functions.     

Activation of the action potential Na+ ionophore of cultured neuroblastoma cells by veratridine and batrachotoxin.

The activation of the action potential Na+ ionophore by veratridine and batrachotoxin is time- and concentration-dependent and completely reversible. Batrachotoxin acts more slowly than veratridine. The concentration dependence of activation at equilibrium suggests reversible interaction of each toxin with a single class of independent sites having dissociation constants at physiologic ion concentrations of 80 plus or minus 13 muM for veratridine and 0.4 plus or minus muM for batrachotoxin. The maximum velocity of Na+ uptake at 50 mM Na+ is 128 plus or minus 12 nmol/min/mg in the presence of batrachotoxin compared to 48 plus or minus 4 nmol/min/mg in the presence of veratridine. Treatment of cells with excess veratridine in addition to batrachotoxin inhibits batrachotoxin-dependent 22-Na+ uptake. The concentration dependence of this inhibition suggests that it reflects competitive displacement of batrachotoxin from its binding site by veratridine. The activation by veratridine and batrachotoxin is inhibited in a competitive manner by divalent cations. The inhibition by divalent cations exhibits significant ion specificity with Mn-2+ greater than Co-2+ greater than Ni-2+ greater than Ca-2+ greater than Mg-2+ greater than Sr-2+. The inhibition constants (KI) for Ca-2+ are 0.84 mM for veratridine-dependent 22-Na+ uptake and 1.2 mM for batrachotoxin-dependent 22-Na+ uptake. The activation by veratridine and batrachotoxin is inhibited in a noncompetitive manner by tetrodotoxin. The apparent KD for tetrodotoxin as 11 plus or minus 1 nM in the presence of 150 mM Na+ and approximately 8.5 nM in 50 mM Na+. Divalent cations do not affect the apparent KD for tetrodotoxin. A hypothesis is presented which suggests that batrachotoxin, veratridine, and divalent cations interact with an activation site associated with the action potential Na+ ionophore, whereas tetrodotoxin interacts with a physically and functionally independent site involved in the transport of monovalent cations by the ionophore.     

Activation by monovalent cations of dissimilatory nitrate reductase in the cells of Pseudomonas denitrificans

Cellular activity of nitrate reductase in Pseudomonas denitrificans which had been grown under denitrifying conditions was increased several times upon incubation of cell suspension with monovalent cations. The enhancement of nitrate reductase activity caused by monovalent cations was ascribed to the activation of the enzyme, since the membrane fraction isolated from the cells after the cation treatment retained the elevated levels of enzyme activity. However, monovalent cations had no effect when added directly to cell-free homogenate, suggesting an important role of some definite structure of membrane in the expression of the effect of monovalent cations.     

Size-dependent allosteric effects of monovalent cations on rabbit liver fructose-1,6-bisphosphatase.

Effects of monovalent cations on the neutral rabbit liver fructose-1,6-bisphosphatase are multifunctional and dependent on their nonhydrated ionic size. (a) The maximal velocity is increased by addition of monovalent cations with the optimum stimulation occurring with a nonhydrated ionic radius of 1.2 A in the presence of a chelating agent such as EDTA. (B) Activation curves are sigmoidal with n values varying from 1.5 to 2.3 as ionic radius of monovalent cation increases. The apparent Ka values from 16.0 to 180 mM, obtained for various monovalent cations, have a linear relationship to ionic radii of cations. (c) At lower concentrations of fructose 1,6-bisphosphate monovalent cations show the inhibitory effect and the apparent Km for fructose 1,6-bisphosphate is increased as the concentration of monovalent cation is increased. A linear relationship is obtained between the slopes of increase in the Km and the reciprocals of ionic volume of monovalent cations. (d) The apparent Ka for Mg2+ is also increased as the concentration of monovalent cation is increased, and a linear relationship is obtained again between the increases in Ka and the reciprocals of ionic volume of monovalent cations. The cooperative nature for Mg2+ saturation is decreased as the Ka increases. (e) The apparent Ki for AMP is also linearly altered as the concentration of monovalent cation is varied. However, the alteration of the Ki is unusual, that is, the smaller cations than K+ increase the Ki (Li+ greater than Na+ greater than NH4+), whereas the larger cations decrease the value ((CH2CH2OH)3N+ greater than Cs+ greater than Rb+). The effect of K+ is insignificant. Alterations in the Ki are also linearly related to the reciprocals of ionic volume of monovalent cations. The cooperative nature for AMP inhibition is decreased or increased as the Ki increased or decreased. (f) In the absence of the chelating agent, the curves for Mg2+ saturation and AMP inhibition were hyperbolic without monovalent cations. By addition of monovalent cation the Ka for Mg+2+ or Ki for AMP is increased and cooperative natures for binding of both ligands are induced. For nonspherical monovalent cations, the application of "functional ionic radius" is proposed. Functional ionic radii of NH4+, (CH2OH)3CNH3+, and (CH2CH2OH)3N+ are estimated to be 1.17, 2.55, and 2.87 A, respectively. The presence of two distinct sites for the actions of monovalent cations is suggested.