The active transport of Mg++ and Mn++ into the yeast cell

Certain bivalent cations, particularly Mg⁺⁺ and Mn⁺⁺, can be absorbed by yeast cells, provided that glucose is available, and that phosphate is also absorbed. The cation absorption is stimulated by potassium in low concentrations, but inhibited by higher concentrations. From the time course studies, it is apparent that the absorption rather than the presence of phosphate and the potassium is the important factor. Competition studies with pairs of cations indicate that binding on the surface of the cell is not a prerequisite to absorption. The absorption mechanism if highly selective for Mg⁺⁺ and Mn⁺⁺, as compared to Ca⁺⁺, Sr⁺⁺, and UO₂⁺⁺, whereas the binding affinity is greatest for UO₂⁺⁺, with little discrimination between Mg⁺⁺, Ca⁺⁺, Mn⁺⁺, and Sr⁺⁺. In contrast to the surface-bound cations which are completely exchangeable, the absorbed cations are not exchangeable. It is concluded that Mg⁺⁺ and Mn⁺⁺ are actively transported into the cell by a mechanism involving a phosphate and a protein constituent.     

Cation dependence of guinea pig epidermal cell spreading

Summary To understand the earliest phases of epidermal cell spreading we have sought a defined in vitro system. We studied the divalent cation dependence of guinea pig epidermal cell spreading in media containing varying concentrations of cations. No spreading occurred in calcium-magnesium-free Dulbecco's modified Eagle's medium (CMF-DME) in the presence of cation-free fetal bovine serum; however, significant spreading occurred if the medium was supplemented with Mg⁺⁺ plus Ca⁺⁺ or Mg⁺⁺ alone. Supplementing with Ca⁺⁺ alone led to much less spreading. These cations in CMF-DME did not support spreading in the absence of serum or the presence of serum albumin. Assaying cell spreading in a simple salt solution consisting of NaCl, KCl, Tris buffer, pH 7.4 plus dialyzed serum and a series of divalent cation supplements (Ca⁺⁺, Mg⁺⁺, Mn⁺⁺, Co⁺⁺, Zn⁺⁺, Ni⁺⁺), showed that only Mg⁺⁺ and Mn⁺⁺, and to a lesser extent, Ca⁺⁺, supported cell spreading. In contrast to Mg⁺⁺, however, Mn⁺⁺ could support spreading in the absence of whole serum if serum albumin were present. Although Mn⁺⁺ plus serum albumin supported more rapid spreading at lower cation concentrations than Mg⁺⁺ plus serum, equal concentrations of Ca⁺⁺ completely blocked the Mn⁺⁺ effect. In contrast to the increasing cell spreading, which occurred in Mg⁺⁺-containing medium with time, cell death occurred in Mn⁺⁺-containing medium by 24 h. Consonant with studies from other laboratories, human foreskin fibroblasts spread in Mn⁺⁺-containing salt solution in the absence of protein supplements. These experiments indicate for epidermal cell spreading that Mg⁺⁺ is the important cation in tissue culture media, that under proper cation conditions epidermal cells do not need a specific spreading protein (i.e. a protein that has been demonstrated to support cell spreading), that Mn⁺⁺ and Mg⁺⁺-induced spreading seem to represent different mechanisms, that fibroblastic and epidermal cells have different cation requirements for in vitro spreading, and that the crucial role cations play in cell spreading remains to be elucidated. This work was supported in part by Public Health Service grant CA34470-01 (KSS) awarded by the National Cancer Institute, Bethesda, Md.     

The effect of anti-ATPase antibodies upon the Ca++ transport of sarcoplasmic reticulum

Sheep or guinea pig antisera against the purified Ca⁺⁺ transport ATPase of sarcoplasmic reticulum inhibit Ca⁺⁺ transport due to a complement-dependent damage of the membrane, which causes massive leakage of Ca⁺⁺. The Ca⁺⁺-activated ATPase activity is only slightly affected even at ten times higher antibody concentration than that required for inhibition of Ca⁺⁺ transport. Antibodies prepared against the Ca⁺⁺ binding protein (C₁ protein) have no influence upon either ATPase activity or Ca⁺⁺ transport and ferritin-labeled anti-C₁ antibodies do not bind to microsomes.     

Synergetic effects of Ca2+ and Cu2+ on phase transition in phosphatidylserine membranes

In complexes of divalent metals with large exchange rate constant (K_H2O) of the coordinated H₂O, such as Ca²⁺ and Cu²⁺, the cubic structure in the ligand field is usually unstable and conformation changes are easily induced. We observed the molecular motion of phosphatidylserine (PS) in an amphipathic solvent (water / methanol / chloroform) by ¹H-NMR and ESR using Ca²⁺ and / or Cu²⁺, which has a similar K_H2O to that of Ca²⁺. We found that Ca²⁺ did not hinder the molecular movements of PS. However, Cu²⁺ reduced the movements of both headgroups and the double bonds in the fatty acids of PS. By addition of both Ca²⁺ and Cu²⁺, phase transition to a soft solid phase in the PS membrane was observed at room temperature. The results indicate that the headgroups are clustered in two-dimensional network with each ligand field displaced from the aqueous phase to the water / oil interface. The structure changes of the polar headgroups after the binding of divalent cations are considered to trigger the phase transition of this acidic phospholipid membrane.     

Role of Ca2+ and Mg2+ in neutrophil hexose transport

The influence of extracellular Ca²⁺ and Mg²⁺ on the transport of 2-deoxy-[³H]glucose into human polymorphonuclear neutrophils was studied. Omission of these cations from the cell suspensions had little effect on resting hexose uptake. Furthermore, the addition of the bivalent cation chelator, EDTA, depressed uptake only slightly. Similarly, neither cation was essential for the enhanced 2-deoxy-D-[³H]glucose uptake stimulated by two chemotactic factors (C5a and $\text{N-}\text{formylmethionylleucylphenylalanine}$) and arachidonic acid: enhanced uptake was only partially depressed by the omission of Ca²⁺ and Mg²⁺ from the suspensions and was still prominent in the presence of EDTA. Two other neutrophil stimulants, the ionophores, A23187 and ionomycin, also enhanced hexose uptake but their actions were heavily dependent upon extracellular bivalent cations and were totally abrogated by EDTA. In all instances, extracellular Ca²⁺, but not Mg²⁺, supported optimal enhanced hexose transport induced by stimuli.Activation of 2-deoxy-D-[³H]glucose uptake by each of the five stimuli was totally blocked by cytochalasin B (a blocker of carrier-mediated hexose transport) and D-glucose but not by L-glucose. The data indicate, therefore, that a variety of neutrophil stimulants activate carrier-mediated hexose transport. Although this transport can be triggered by the movement of extracellular Ca²⁺ into the cell (as exemplified by the action of the two ionophores), such Ca²⁺ movement is not required for the actions of chemotactic factors or arachidonic acid. Other mechanisms, such as a rearrangement of intracellular Ca²⁺, may be involved in mediating the activation of hexose transport induced by the latter stimuli.     

Triple helix formation and disulphide bonding during the biosynthesis of glomerular basement membrane collagen.

White erythrocyte membranes, or ghosts, were monoconcave discocytes when incubated in 50mM N-tris (hydroxymethyl) methyl-2-aminoethane sulfonic acid titrated to pH 7.4 with triethanolamine. If 3mM MgCl₂ was included in the incubation medium, the ghosts were predominantly echinocytes. The echinocytic form could also be induced by Co⁺⁺, Ni⁺⁺, Li⁺, Na⁺, K⁺, $\text{NH}{}_4{}^{\mathrm{+}}$ and tetramethylammonium ion, all as chloride salts. The concentration of cation necessary for 50% of the ghosts to be echinocytes was correlated with the hydrated charge density of the cation with the most highly charged cations being the most effective. The cations Ca⁺⁺, Sr⁺⁺, Ba⁺⁺ and La⁺⁺⁺, (also as chloride salts) did not induce the normal echinocytic form, but at high levels induced a few misshapen forms with some resemblance to echinocytes. Instead Ca⁺⁺, Sr⁺⁺, Ba⁺⁺ and La⁺⁺⁺ suppressed the formation of echinocytes in the presence of Mg⁺⁺ and other ions. This suggests the presence of a specific Ca⁺⁺ binding site important to shape control in the erythrocyte membrane.     

31P NMR lineshapes of β-P (ATP) in the presence of mg2+ and ca2+ : estimate of exchange rates

The ³¹ P NMR chemical shift of β-P of adenosine triphosphate (ATP) undergoes a substantial change (2̃–3 ppm) upon chelation of divalent ions such as Mg²⁺ or Ca²⁺. In the presence of nonsaturating amounts of Mg²⁺ or Ca²⁺, the lineshape of this resonance depends on the characteristic association and dissociation rates of these metal-ATP complexes. A procedure for computer simulation of this lineshape is outlined. A comparison of computer-simulated lineshapes with the experimental lineshapes obtained at 121 MHz was used to determine the following dissociation rate of Mg²⁺ and Ca²⁺ from their ATP complexes at 20°C and pH 8.0: Ca²⁺, > 3 × 10⁵ s^?1 (Hepes buffer); Mg²⁺, 1200 s^-1 (no buffer), 1000 s^-1 (Tris buffer) and 2100 s^?1 (Hepes buffer). The limits of error are ± 10% in these values. For the Mg²⁺ complexes, the rates were determined as a function of temperature to obtain activation energies (with a maximum deviation of 10% in the least-squares fit): 8.1 $\text{Kcal}\text{mole}$ (no buffer and Hepes buffer) and 6.8 $\text{kcal}\text{mole}$ (Tris buffer). Lineshapes of the β-Presonance simulated as a function of Mg²⁺ concentration, using 2100 s^?1 for the dissociation rate, are also presented. The computer simulation of lineshapes offers a reliable and straightforward method for the determination of exchange rates of diamagnetic cations from their ATP complexes, under a variety of sample conditions.     

The effect of Mg ++ on the conformation of the Ca ++ -binding component of troponin

Mg⁺⁺ like Ca⁺⁺ induces a conformational change in the Ca⁺⁺-binding component of troponin. However, this change is only 36 % of the change in fluorescence intensity and 80 % of the change in optical rotation induced by Ca⁺⁺. The apparent binding constant of Mg⁺⁺ to the Ca⁺⁺-binding component is 5 × 10³ M⁻¹, much smaller than that of Ca⁺⁺. Circular dichroism measurements show that these changes are simple helix-coil transitions. Unlike the Ca⁺⁺-induced conformational change, the Mg⁺⁺-induced change cannot be propagated to other muscle proteins, and therefore has no physiological meaning.     

Selectivity of interaction of univalent cations with mammalian ribosomes studied by equilibrium dialysis in the presence of the K+ analogue, 204Tl+

The interaction of K⁺ with mammalian ribosomes was studied by equilibrium dialysis and compared with that of other univalent cations. The heavy K⁺ analogue, Tl⁺, binds more firmly than K⁺ to ribosomes and, unlike K⁺, has a practically useful isotope. With ²⁰⁴Tl⁺ as a marker of K⁺-selective binding the ribosome-cation interaction could be followed down to levels below 0.1 average Tl⁺-occupied site per ribosome. The Tl⁺/ribosome ratio varied with the free Tl⁺ concentration in a multiple way. At high Tl⁺ saturation Tl⁺ was easily displaced by Mg²⁺. With decreasing Tl⁺ saturation the competitive activity of Mg⁺⁺ was strikingly reduced, indicating that Tl⁺ and Mg⁺⁺ compete with different efficiency for different classes of sites.The experiments on univalent cations were performed at 1.5 mM Mg²⁺ under two complementary conditions: (1) Ribosomes were pretreated with 5 × 10^?2, 5 × 10^?3, and 5 × 10^?4 M LiNO₃, NaNO₃, KNO₃, and CsNO₃, and then equilibrated with different concentrations of ²⁰⁴TlNO₃ in the same buffers. (2) Ribosomes were pretreated with 10^?2, 10^?4, and 10^?6 M ²⁰⁴TlNO₃, and then equilibrated with different concentrations of LiNO₃, NaNO₃, KNO₃, and CsNO₃ (displacement experiments). At high Tl⁺ saturation Na⁺ and Li⁺ were about as active as K⁺ and Cs⁺ in competing with ²⁰⁴Tl⁺. With decreasing Tl⁺ saturation a differentiation occurred in favor of K⁺ and Cs⁺, with some preference for K⁺. It is concluded that ribosomes contain a limited number of sites with pronounced ion specificity. Of physiological cations K⁺ is most firmly bound to these sites.     

The effect of divalent metal ions on the activity of Mg++ depleted ribulose-1,5-bisphosphate oxygenase

Ribulose-1,5-bisphosphate carboxylase-oxygenase is deactivated by removal of Mg⁺⁺. The enzyme activities can be restored to a different extent by the addition of various divalent ions in the presence of CO₂. Incubation with Mg⁺⁺ and CO₂ restores both enzyme activities, whereas, the treatment of the enzyme with the transition metal ions (Mn⁺⁺, Co⁺⁺, and Ni⁺⁺) and CO₂ fully reactivates the oxygenase: however, the carboxylase activity remains low. In experiments where CO₂-free conditions were conscientiously maintained, no reactivation of RuBP oxygenase was observed, although Mn⁺⁺ ions were present. Other divalent cations such as Ca⁺⁺ and Zn⁺⁺, restore neither the carboxylase nor the oxygenase reaction. Furthermore, the addition of Mn⁺⁺ to the Mg⁺⁺ and CO₂ preactivated enzyme significantly inhibited carboxylase reactions, but increased the oxygenase reaction.Abbreviation RuBP ribulose-1,5-bisphosphate. The enyme unit for RuBP carboxylase is defined as mol CO₂ fixed·min^-1 and for the RuBP oxygenase as mol O₂ consumed · min^-1     

QUANTITATIVE STUDIES OF PHAGOCYTOSIS : Kinetic Effects of Cations and Heat-Labile Opsonin

Kinetic analysis of the initial ingestion rate of albumin-coated paraffin oil particles by human granulocytes and rabbit alveolar macrophages was undertaken to study the mechanism of action of cations and of heat-labile opsonin on engulfment. The rate of uptake of the particles was stimulated by Ca⁺⁺, Mg⁺⁺, Mn⁺⁺, or Co⁺⁺. At high concentrations (> 20 mM) Ca⁺⁺ and Mg⁺⁺ inhibited the rate of ingestion. Treatment of the particles with fresh serum (heat-labile opsonin) also stimulated the rate of ingestion. ¹²⁵I-labeled C3 was bound to the particles during opsonization. C3-deficient human serum lacked opsonic activity, which was restored by addition of purified C3. Normal, C2-deficient, and hereditary angioneurotic edema sera had equivalent opsonic activity. The serum opsonic activity thus involved C3 fixation to the particles by means of the properdin system. Although Mg⁺⁺ and heat-labile opsonin both accelerated the maximal rates of ingestion of the particles, neither altered the particle concentrations associated with one-half maximal ingestion rates. Opsonization of the particles markedly diminished the concentrations of divalent cations causing both stimulatory and inhibitory effects on ingestion rates and altered the shapes of the cation activation curves. ⁴⁵Ca was not bound to the particles during opsonization. The results are consistent with a mechanism whereby divalent cations and heat-labile opsonin activate ingestion by stimulating the work of engulfment rather than by merely enhancing cell-particle affinity, and whereby heat-labile opsonin acts by potentiating the effects of divalent cations.     

3H-mepyramine binding to histamine H1-receptors in guinea pig lung: Characteristics and regulation by ions

The antogonist [³H]-mepyramine is used to label histamine H₁-receptors in guinea pig lung. Scatchard analysis reveals two classes of binding sites. Monovalent cations decrease steady-state binding (Na⁺ > Li⁺ > K⁺), while divalent cations (Mg⁺⁺, Ca⁺⁺, Mn⁺⁺, Ba⁺⁺) exhibit a biphasic curve, increasing binding at low concentrations and decreasing it at higher levels. Na⁺ decreases both affinity and number of binding sites. Dissociation curve shows two components, and Na⁺ accelerates the rate of dissociation of the slower component. GTP does not affect the binding of the antagonist ³H-Mepyramine.     

Effect of magnesium and calcium ions on blocking of synaptic transmission by adenosine in isolated rat hippocampal slices

Dependence of the inhibitory action of adenosine on the extracellular composite EPSP on the concentrations of Mg and Ca cations in the medium was investigated in isolated slices of rat hippocampusin vitro. Extracellular EPSPs were derived in the region of apical dendrites of pyramidal cells in area CA₁ during stimulation of Schaffer's collaterals. The blocking action of bivalent cations (an increase in Mg⁺⁺ or a decrease in Ca⁺⁺) developed almost five times more slowly than the action of adenosine. An increase in the external Mg⁺⁺ concentration potentiated whereas a decrease weakened the inhibitory action of adenosine. Ca⁺⁺ ions had the opposite effect. Antagonistic relations were exhibited between Mg⁺⁺ and Ca⁺⁺ ions. Analysis of dose-response curves for adenosine showed that during a simultaneous increase in the extracellular Ca⁺⁺ and decrease in Mg⁺⁺ concentrations, not only was the maximal effect of adenosine reduced, but so also was its binding constant with the receptor. The results suggest that antagonism between Ca cations and adenosine is mixed in character — both competitive and noncompetitive. The possible mechanism of the inhibitory action of adenosine on synaptic transmission and the role of bivalent cations in this process are discussed.A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 16, No. 4, pp. 532–539, July–August, 1984.     

Localization of (Ca2+ + Mg2+)-ATPase,Ca2+ pump and other ATPase activities in cardiac sarcolemma

N-Ethylmaleimide was employed as a surface label for sarcolemmal proteins after demonstrating that it does not penetrate to the intracellular space at concentrations below 1·10^?4 M. The sarcolemmal markers, ouabain-sensitive (Na⁺ + K⁺)-ATPase and Na⁺/Ca²⁺-exchange activities, were inhibited in N-ethylmaleimide perfused hearts. Intracellular activities such as creatine phosphokinase, glutamate-oxaloacetate transaminase and the internal phosphatase site of the Na⁺ pump (K⁺-p-nitrophosphatase) were not affected. Almost 20% of the (Ca²⁺ + Mg²⁺)-ATPase and Ca²⁺ pump were inhibited indicating the localization of a portion of this activity in the sarcolemma. Sarcolemma purified by a recent method (Morcos, N.C. and Drummond, G.I. (1980) Biochim. Biophys. Acta 598, 27–39) from N-ethylmaleimide-perfused hearts showed loss of approx. 85% of its (Ca²⁺ + Mg²⁺-ATPase and Ca²⁺ pump compared to control hearts. (Ca²⁺ + Mg²⁺)-ATPase and Ca²⁺ pump activities showed two classes of sensitivity to vanadate ion inhibition. The high vanadate affinity class ($\text{K}{}_{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}$ for inhibition approx. 1.5 μM) may be localized in the sarcolemma and represented approx. 20% of the total inhibitable activity in agreement with estimates from N-ethylmaleimide studies. Sucrose density fractionation indicated that only a small portion of Mg²⁺-ATPase and Ca²⁺-ATPase may be associated with the sarcolemma. The major portion of these activities seems to be associated with high density particles.     

Thermodynamic and kinetic parameters of ion condensation to polynucleotides: Outer sphere complex formed by Mg++ ions

The coupling of ion binding to the single strand helix—coil transition in poly (A) and poly(C) is used to obtain information about both processes by ion titration and field-jump relaxation methods. Characterisation of the field-jump relaxation in poly(C) at various concentrations of monovalent ions leads to the evaluation of a stability constant K = 71 M^?1 for the ion binding to the polymer. The rate constant of helix formation is found to be 1.3 × 10⁷ s^?1, whereas the dissociation rate is 1.0 × 10⁶ s^?1. Similar data are presented for poly (A) and poly (dA).The interaction of Mg⁺⁺ and Ca⁺⁺ with poly (A) and poly (C) is measured by a titration method using the polymer absorbance for the indication of binding. The data can be represented by a model with independent binding “sites”. The stability constants increase with decreasing salt concentration from 2.7 × 10⁴ M^?1 at medium ionic strengths up to 2.7 × 10⁷ M^?1 at low ionic strength. The number of ions bound per nucleotide residue is in the range 0.2 to 0.3. Relaxation time constants associated with Mg⁺⁺ binding are characterised over a broad range of Mg⁺⁺ concentrations from 5 μM to 500 μM. The observed concentration dependence supports the conclusion on the number of binding places inferred from equilibrium titrations. The rate of Mg⁺⁺ and Ca⁺⁺ association to the polymer is close to the limit of diffusion control (k_R = 1 × 10¹⁰ to 2 × 10¹⁰ M^?1 s^?1). This high rate demonstrates that Mg⁺⁺ and Ca⁺⁺ ions do not form inner-sphere complexes with the polynucleotides. Apparently the distance between two adjacent phosphates is too large for a simultaneous site binding of Mg⁺⁺ or Ca⁺⁺, and inner sphere complexation at a single phosphate seems to be too weak. The data support the view that the ions like Mg⁺⁺ and Ca⁺⁺ surround the polynucleotides in the form of a mobile ion cloud without site binding.     

Possible role of a peroxidative system in melanin synthesis inVerticillium

Manometric tests demonstrated phenolase activity in potato and mushroom extracts but little in extracts from a microsclerotial isolate ofVerticillium albo-atrum. The purpurogallin test indicated the presence of peroxidase activity in theseVerticillium extracts. An assay for an enzyme system which produced dark pigment from catechol was developed. Mn⁺⁺ stimulated pigment synthesis about twice as much as Mg⁺⁺ or Ca⁺⁺. Other cations, Co⁺⁺, Ni⁺⁺, Zn⁺⁺, Cu⁺⁺ and Fe⁺⁺ had less effect. The cell-free enzyme system containing H₂O₂ and Mn⁺⁺ produced dark-colored products from catechol, dopa, andp-phenylenediamine. Pyrogallol yielded a bright yellow color. Chemicals which did not yield colored products as a result of enzyme action included aniline, ascorbic acid, chlorogenic acid,p-cresol, gallic acid, hydroquinone, phenol, phenylalanine, protocatechuic acid, resorcinol, shikimic acid, and tyrosine. In view of these results and the failure of others to demonstrate more than weak phenolase activity inVerticillium, we conclude that a peroxidation probably initiates most melanin synthesis inVerticillium.     

Interaction of Ca2+ with (Na+ + K+)-ATPase: Properties of the Ca2+-stimulated phosphatase activity

Ca²⁺ inhibited the Mg²⁺-dependent and K⁺-stimulated p-nitrophenylphosphatase activity of a highly purified preparation of dog kidney (Na⁺ + K⁺)-ATPase. In the absence of K⁺, however, a Mg²⁺-dependent and Ca²⁺-stimulated phosphatase was observed, the maximal velocity of which, at pH 7.2, was about 20% of that of the K⁺-stimulated phosphatase. The Ca²⁺-stimulated phosphatase, like the K⁺-stimulated activity, was inhibited by either ouabain or Na⁺ or ATP. Ouabain sensitivity was decreased with increase in Ca²⁺, but the K_0.5 values of the inhibitory effects of Na⁺ and ATP were independent of Ca²⁺ concentration. Optimal pH was 7.0 for Ca²⁺-stimulated activity, and 7.8–8.2 for the K⁺-stimulated activity. The ratio of the two activities was the same in several enzyme preparations in different states of purity. The data indicate that (a) Ca²⁺-stimulated phosphatase is catalyzed by (Na⁺ + K⁺)-ATPase; (b) there is a site of Ca²⁺ action different from the site at which Ca²⁺ inhibits in competition with Mg²⁺; and (c) Ca²⁺ stimulation can not be explained easily by the action of Ca²⁺ at either the Na⁺ site or the K⁺ site.     

Effect of metal ions (Li+, Na+, K+, Mg2+, Ca2+, Ni2+, Cu2+ and Zn2+) and water coordination on the structure and properties of l-histidine and zwitterionic l-histidine

Interactions between metal ions and amino acids are common both in solution and in the gas phase. The effect of metal ions and water on the structure of l-histidine is examined. The effect of metal ions (Li⁺, Na⁺, K⁺, Mg²⁺, Ca²⁺, Ni²⁺, Cu²⁺ and Zn²⁺) and water on structures of His·M(H₂O)m, m = 0.1 complexes have been determined theoretically employing density functional theories using extended basis sets. Of the five stable complexes investigated the relative stability of the gas-phase complexes computed with DFT methods (with one exception of K⁺ systems) suggest metallic complexes of the neutral l-histidine to be the most stable species. The calculations of monohydrated systems show that even one water molecule has a profound effect on the relative stability of individual complexes. Proton dissociation enthalpies and Gibbs energies of l-histidine in the presence of the metal cations Li⁺, Na⁺, K⁺, Mg²⁺, Ca²⁺, Ni²⁺, Cu²⁺ and Zn²⁺ were also computed. Its gas-phase acidity considerably increases upon chelation. Of the Lewis acids investigated, the strongest affinity to l-histidine is exhibited by the Cu²⁺ cation. The computed Gibbs energies ΔG are negative, span a rather broad energy interval (from ?130 to ?1,300 kJ/mol), and upon hydration are appreciably lowered.     

Über die Wirkung von ADP und einigen Kationen auf die Rotationsströmung in den Wurzelhaaren der Gerste (Hordeum vulgare L.)

Zusammenfassung In getrennten Versuchen wurde die Wirkung von ADP, Ca⁺⁺, Mg⁺⁺, K⁺ und Cu⁺⁺ auf die Rotationsströmung in den Wurzelhaaren der Gerste (Hordetim vulgare L.) untersucht. Das in verschiedenen Konzentrationen fortdauernd verabreichte ADP bedingte eine Stimulation der Plasmaströmung. Die Beschleunigung der Rotationsströmung war der ADP-Konzentration gegenüber umgekehrt proportional (Abb. 3).Von den untersuchten Kationen hatte nur Ca⁺⁺ (1·10^–3 Mol) eine Stimulationswirkung. Diese Stimulationswirkung wird der Aktivierung eines Enzyms bzw. eines kontraktilen Proteins mit ATPase-Eigenschaften zugeschrieben.Die Rolle von ADP und einigen Kationen bei der Stimulation der Rotation wurde dann mit Hilfe einer gemischten Behandlung untersucht. Diese bestand in der gleichzeitigen Verabreichung von ADP (1·10^–6 Mol) und CaCl₂, MgCl₂, KCl (1 · 10^–3 Mol) oder CuCl₂ (1·10^–6 Mol). Es wurde festgestellt, daß Mg⁺⁺ und Ca⁺⁺ eine antagonistische Wirkung ausüben. Ca⁺⁺ hebt die durch ADP induzierte Stimulation auf und reduziert die Rotationsgeschwindigkeit plötzlich bis auf den Kontrollwert. Die Mg⁺⁺-Wirkung bewirkt, nach einer zeitweiligen Beibehaltung der Stimulation, ebenfalls eine Abnahme der Geschwindigkeit. K⁺ hat eine ähnliche Wirkung wie Ca⁺⁺. Cu⁺⁺ beeinträchtigt die ADP-induzierte Stimulation in geringem Maße.Die gleichzeitige Einwirkung von ADP und einigen Kationen erlaubt die Aufstellung folgender Hypothese. Die Rotationsstimulation erfolgt dank dem ATP, das auf Kosten des von außen absorbierten ADP in den Mitochondrien synthetisiert wird. Die zusätzliche ATP-Synthese kann durch gleichzeitige Ca⁺⁺-Behandlung unterbunden werden. NachHanson und Mitarb, sollen Ca⁺⁺ und ADP um ein phosphoryliertes Zwischenprodukt in Kompetition treten, so daß es zu einer Ansammlung von Ca⁺⁺ und P_a in der Zelle kommt. Andererseits könnte teilweise auch die aktive, energieverbrauchende Salzabsorption die Geschwindigkeitsabnahme der Rotation bei gemischter Behandlung erklären.

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The effect of ADP and some cations on rotational streaming in barley (Hordeum vulgare L.) root hairs

Summary The effect of ADP, Ca⁺⁺, Mg⁺⁺, K⁺, and Cu⁺⁺ upon rotational streaming within barley (Hordeum vulgäre L.) root hairs was separately studied. It was shown that various solutions of ADP may stimulate the streaming after continuous treatment. The rate increase of the rotational streaming was inverse proportional to ADP concentration (Fig. 3).From the investigated cations only Ca⁺⁺ (1·10^–3M) caused a stimulation of streaming after continuous treatment. This effect is probably due to enzymic activation of a contractile proteine which has ATPase feature.The role of ADP and of the investigated cations in the stimulation of the rotational streaming was studied by means of mixed treatment. This kind of treatment consists in a simultaneous administration of ADP (1 · 10^–6M) and CaCl₂, MgCl₂, KCl (1 · 10^–3M), or CuCl₂ (1 · 10^–6M) solutions. Ca⁺⁺ and Mg⁺⁺ showed an antagonistic action. Ca⁺⁺ brings about an immediately suppress of ADP induced stimulation. Suddenly the rate of streaming comes back to control. Mg⁺⁺ after a temporary maintaining of stimulation, also causes the lowering of the streaming. The action of K⁺ was very similar to those of Ca⁺⁺. Cu⁺⁺ changes to a little extent the stimulation caused by ADP.The simultaneous action of ADP and of the investigated cations allow us to express the following hypothesis. The stimulation of the rotational streaming after ADP treatment probably is due to ATP synthetized in mitochondria on the account of ADP. The additional synthesis of ATP can be prevented by simultaneous administration of Ca⁺⁺. According toHanson and his coworkers Ca⁺⁺ would compete with ADP for a phosphorylated intermediate product. From a such competition would result the Ca⁺⁺ and P_i accumulation. The active uptake of salts which require energy would also explain the lowering of the rotational streaming rate after the mixed treatment.