Low Concentrations Of Na Research Articles

Na+-mediated piezoprotection in Rhodotorula rubra.

Sodium concentrations as low as 2 mM exerted a significant protective effect on the high-pressure inactivation (160-210 MPa) of Rhodotorula rubra at pH 6.5, but not on two other yeasts tested (Schizosaccharomyces pombe and Saccharomyces cerevisiae). A piezoprotective effect of similar magnitude was observed with Li+ (2 and 10 mM), and at elevated pH (8.0-9.0), but no effect was seen with K+, Ca2+, Mg2+, Mn2+, or NH4(+). Intracellular Na+ levels in cells exposed to low concentrations of Na+ or to pH 8.0-9.0 provided evidence for the involvement of a plasma membrane Na+/H+ antiporter and a correlation between intracellular Na+ levels and pressure resistance. The results support the hypothesis that moderate high pressure causes indirect cell death in R. rubra by inducing cytosolic acidification.

The luteinizing hormone receptor: influence of buffer composition on ligand binding and signaling of wild type and mutant receptors

There is evidence that ligand binding to and ligand-mediated signaling by the luteinizing hormone receptor (LHR) are influenced by buffer conditions, including ionic type and strength, an issue that becomes important in comparing functional parameters obtained on receptor mutants under different conditions. In order to study this phenomenon, we performed binding (kinetic and saturation) and signaling studies of human chorionic gonadotropin (hCG) with wild type (wt) LHR and several mutants expressed in COS-7 cells using two common buffer systems. One buffer was of low ionic strength and contained a low concentration of Na +, while the other had a near-physiological concentration of Na +. Emphasis was placed on mutations of two amino acid residues in the hinge region of the ectodomain (E332 and D333). It was found that the buffer of higher ionic strength, primarily from Na +, led to an increase of about 4-fold in the K d of hCG binding to wt and mutant LHRs. The reduced binding affinities were attributable to a comparable reduction in the rate constants of association, with no significant differences in the calculated rate constants of dissociation in the two buffers. Analysis of the signaling properties of these mutants showed that, when corrected for the amount of hCG bound under the conditions of the signaling assay, the maximal ligand-mediated cAMP produced in cells maintained in the buffer of low ionic strength was comparable for wt LHR and the mutants, only the D333A mutant being somewhat elevated. In the buffer of higher ionic strength, however, the response by wt LHR was significantly greater than that of the mutants. These results show that E332 and D333 are important in hormone-mediated signaling, but only in the buffer of higher Na + concentration. In addition to mutants of these two residues, the buffer of higher ionic strength also led to reduced binding to a number of mutants throughout the receptor. Since these mutants included additional replacements in the ectodomain and transmembrane helices 6 and 7, the general nature of the buffer effect on wt and mutant LHRs suggests that electrostatic effects are contributing to ligand binding and/or that the LHR ectodomain may exist in two conformations, one being more accessible to ligand at reduced ionic strength.

Raman microspectroscopic study of effects of Na(I) and Mg(II) ions on low pH induced DNA structural changes.

In this work a confocal Raman microspectrometer is used to investigate the influence of Na(+) and Mg(2+) ions on the DNA structural changes induced by low pH. Measurements are carried out on calf thymus DNA at neutral pH (7) and pH 3 in the presence of low and high concentrations of Na(+) and Mg(2+) ions, respectively. It is found that low concentrations of Na(+) ions do not protect DNA against binding of H(+). High concentrations of monovalent ions can prevent protonation of the DNA double helix. Our Raman spectra show that low concentrations of Mg(2+) ions partly protect DNA against protonation of cytosine (line at 1262 cm(-1)) but do not protect adenine and guanine N(7) against binding of H(+) (characteristic lines at 1304 and 1488 cm(-1), respectively). High concentrations of Mg(2+) can prevent protonation of cytosine and protonation of adenine (disruption of AT pairs). By analyzing the line at 1488 cm(-1), which obtains most of its intensity from a guanine vibration, high magnesium salt protect the N(7) of guanine against protonation. A high salt concentration can prevent protonation of guanine, cytosine, and adenine in DNA. Higher salt concentrations cause less DNA protonation than lower salt concentrations. Magnesium ions are found to be more effective in protecting DNA against binding of H(+) as compared with calcium ions presented in a previous study. Divalent metal cations (Mg(2+), Ca(2+)) are more effective in protecting DNA against protonation than monovalent ions (Na(+)).

Blockers of sodium and calcium entry protect axons from nitric oxide-mediated degeneration.

Axonal degeneration can be an important cause of permanent disability in neurological disorders in which inflammation is prominent, including multiple sclerosis and Guillain-Barré syndrome. The mechanisms responsible for the degeneration remain unclear, but it is likely that axons succumb to factors produced at the site of inflammation, such as nitric oxide (NO). We previously have shown that axons exposed to NO in vivo can undergo degeneration, especially if the axons are electrically active during NO exposure. The axons may degenerate because NO can inhibit mitochondrial respiration, leading to intraaxonal accumulation of Na(+) and Ca(2+) ions. Here, we show that axons can be protected from NO-mediated damage using low concentrations of Na(+) channel blockers, or an inhibitor of Na(+)/Ca(2+) exchange. Our findings suggest a new strategy for axonal protection in an inflammatory environment, which may be effective in preventing the accumulation of permanent disability in patients with neuroinflammatory disorders.

Mechanism of formation of a productive molten globule form of barstar.

Structural analysis of the initial steps in protein folding is difficult because of the swiftness with which these steps occur. Hence, the link between initial polypeptide chain collapse and formation of secondary and other specific structures remains poorly understood. Here, an equilibrium model has been developed for characterizing the initial steps of folding of the small protein barstar, which lead to the formation of a productive molten globule in the folding pathway. In this model, the high-pH-unfolded form (D form) of barstar, which is shown to be as unstructured as the urea-denatured form, is transformed progressively into a molten globule B form by incremental addition of the salt Na(2)SO(4) at pH 12. At very low concentrations of Na(2)SO(4), the D form collapses into a pre-molten globule (P) form, whose volume exceeds that of the native (N) state by only 20%, and which lacks any specific structure as determined by far- and near-UV circular dichroism. At higher concentrations of Na(2)SO(4), the P form transforms into the molten globule (B) form in a highly noncooperative transition populated by an ensemble of at least two intermediates. The B form is a dry molten globule in which water is excluded from the core, and in which secondary structure develops to 65% and tertiary contacts develop to 40%, relative to that of the native protein. Kinetic refolding experiments carried out at pH 7 and at high Na(2)SO(4) concentrations, in which the rate of folding of the D form to the N state is compared to that of the B form to the N state, indicate conclusively that the B form is a productive intermediate that forms on the direct pathway of folding from the D form to the N state.

The effect of high concentration of sodium and potassium ion on motility of human sperm preserved in electrolyte-free solution

To assess the effect of high concentration of sodium and potassium ion on the motilities of human sperm following the preservation in electrolyte-free solution. Semen samples were obtained from patients attending our infertility clinic. The motilities of their sperm were more than 40%. Ejaculated sperm were washed by using the electrolyte-free Percoll gradient and then preserved in electrolyte-free solution at 4 degrees C for a week. The preserved sperm was incubated and analyzed after the addition of electrolyte solutions under acid or alkaline condition. The sperm were continuously preserved for a day at room temperature and analyzed. The sperm was by the addition of 35-135 mM Na+ or 5-135 mM K+ in acid solutions. Under the alkaline conditions, sperm were reactivated without Na+ or K+. However, the addition of 135 mM Na+ or K+ significantly decreased in sperm motilities. The some sperm in the solution containing low concentration of Na+ or K+ ions maintained their motilities for a day at room temperature. However, all sperm lost their motilities in the 135 mM Na+ or K+ solutions. The high concentration of Na+ or K+ ions had detrimental effects on motilities of sperm following the preservation in electrolyte-free solution.

Hydrodesulfurization of thiophene over synthetic cobalt-containing smectite-like mesoporous materials

Mesoporous smectite-like materials containing cobalt, SM(Co), were synthesized by a hydrothermal method under different conditions. The materials were used as catalysts for hydrodesulfurization (HDS) of thiophene. The SM(Co) sample is a new type of active HDS catalyst. The activity depends on the synthetic conditions used, but the product distribution does not change so much, giving trans-2-butene, cis-2-butene, and 1-butene with a minor product of n-butane. The high HDS activity of SM(Co) samples may be explained by higher degrees of cobalt dispersion due to the method of preparation used. In addition, the treatment of SM(Co) samples with ammonia solution is effective in enhancing their HDS activities, in particular for originally less active ones. The treatment removes Na + species involved and this may suppress structural changes of SM(Co) samples by HDS reactions. The ammonia-treated samples maintain high surface area and include much lower concentrations of Na + species, which would have a negative effect on the activity, and so they indicate enhanced HDS activity.

Amino acids involved in sodium interaction of murine type II Na(+)-P(i) cotransporters expressed in Xenopus oocytes.

Type IIa and IIb Na+-Pi cotransporters are highly conserved proteins expressed in brush border membranes of proximal tubules and small intestine, respectively. The kinetics of IIa and IIb differ significantly: type IIb is saturated at lower concentrations of Na+ and Pi. To define the domain responsible for the difference in Na+ affinity we constructed several mouse IIa-IIb chimeras as well as site-directed mutagenized cotransporters. Pi uptake activity was determined after injection of cRNAs into Xenopus laevis oocytes. From the chimera experiments we concluded that the domain containing part of the second intracellular loop, the fifth transmembrane domain (TD) and part of the third extracellular loop determines the specific Na+ activation properties for both types of cotransporter. Within this domain only a few residues located in the fifth TD are not conserved between type IIa and IIb. Site-directed mutagenesis on non-conserved residues was performed. Substitution of F402 of IIa by the corresponding L418 from IIb yielded a cotransporter that behaved like the IIb. On the other hand, substitution of the specific L418 of IIb by the corresponding F402 of IIa produced a cotransporter with a Na+ activation similar to IIa. (Single letter amino acid nomenclature is used throughout the paper.) These data suggest that the specific Na+ activation properties exhibited by type IIa and type IIb Na+-Pi cotransporters are at least in part due to the presence of a specific amino acid (F402 in IIa, and L418 in IIb) within the fifth TD of the protein.

Copper transfer modeling through a nanofiltration membrane in the case of ternary aqueous solution

Mixed solutions containing copper salts were separated using a nanofiltration membrane. For mixed electrolyte solutions with the same co-ion, the rejection of copper was shown to depend strongly on the nature of the second counter-ion. In the presence of H 3O + or at low concentration of Na +, copper ions are completely rejected, while in the presence of Ca 2+, their transfer is slightly improved. The extended Nernst Planck equation was applied to modelize experimental results using specific calculated transfer parameters. The variations of the concentration and the electrostatic potential were considered to be linear through the membrane. Moreover, the solute concentration near the membrane was assumed to be equal to the feed solution concentration. Calculated copper rejections are in good agreement with experimental results.

The effect of low concentrations of sodium on potassium uptake and growth of wheat

Sodium is a beneficial mineral for some plant species when external concentrations are low. The role of Na+ in energising K+ acquisition in terrestrial plants has recently been suggested because of evidence demonstrating that wheat root cells express a high-affinity Na+-energised K+ symporter. To determine whether low concentrations of Na+ improve the K+ nutrition and growth of wheat, long-term growth and short-term tracer flux experiments were conducted. Long-term growth experiments were conducted over a range of K+ concentrations, at acidic and alkaline pH, with and without 500 µM NaCl. Plant biomass and tissue Na+ and K+ content was measured. Short-term experi-ments were conducted using tracers to determine whether low concentrations of Na+ or K+ stimulate Rb+ or Na+ uptake, respectively. Sodium stimulated the growth of wheat only at low (20 µM) external K+ in one of the long-term experiments, but not in two other experiments. Na+ did not stimulate Rb+ uptake, but K+ stimulated Na+ uptake in short-term tracer flux experiments. The results suggest that low concentrations of Na+ do not increase K+ uptake to a large extent, and only when light levels are low does Na+ have a beneficial effect on the growth of wheat.

Hydrological flow paths controlling stream chemistry in Japanese forested watersheds

Water sources and flow paths contributing to stream chemistry were evaluated in four Japanese forested watersheds with steep topography (slopes ≥30°). Stream chemistry during periods without rainfall and during events with less than 100 mm of precipitation was similar to seepage water chemistry, but markedly different from that of soil water which had higher concentrations of NO−3 and Ca2+ and lower concentrations of Na+ and HCO−3. Also, stream Cl− concentrations in a Cl−-treated watershed did not increase either during events with less than 100 mm of total rainfall or at baseflow conditions, even three years after the Cl− treatment. These results suggest that groundwater within bedrock fissures of Paleozoic strata had a long residence time and was a major contributor to steam water under baseflow conditions and even during small precipitation events (≤100 mm). In contrast, for large precipitation events (≥100 mm), stream chemistry became more similar to soil water chemistry, especially within the steepest watershed. Also, for large precipitation events, stream Cl− concentrations in the Cl−-treated watershed increased markedly. These results suggest that soil water was a major contributor to stream waters only during these large events. Copyright © 1999 John Wiley & Sons, Ltd.

The contribution of water to the selectivity of pyruvate kinase for Na+ and K+.

For many years it has been known that K+ is an essential activator of pyruvate kinase [Kachmar, J. F. & Boyer, P. D. (1953) J. Biol. Chem. 200, 669-683] and that Na+ induces relatively small enhancements of activity. The effect of these two alkali metal ions on the activity of pyruvate kinase entrapped in the low water environment of reverse 'micelles formed with cetyltrimethylammonium, hexanol, n-octane and various water concentrations was studied. In reverse micelles with 3.6% water, the activity with 7 mM Na+ is more than 82 times higher than in aqueous solution with an equivalent Na+ concentration. As the concentration of water in reverse micelles is raised, the activating effect of relatively low concentrations of Na+ (or K+) decreases simultaneously to a more than 100-fold increase in the concentration of Na+ or K+ required for attaining half-maximal activation. Similar results were obtained with NH4+, Rb+ and Cs+. Therefore, the amount of water in the system is critical for observing activation by alkali metal ions. In fact, the concentration of Na+ required for half-maximal activation in standard aqueous media is higher than the concentrations that can be experimentally assayed. As evidenced from fluorescence and kinetic data, it appears that the entrapment of pyruvate kinase in reverse micelles does not produce gross structural alterations. Therefore, it is suggested that in conventional aqueous systems, the basis of the high discrimination between Na+ and K+ by pyruvate kinase is the higher energy required for desolvating Na+. Nevertheless, at all the water concentrations studied, the activities reached with K+ were higher than with Na+ which suggests that the Na+ form of the enzyme has a lower catalytic capacity than the K+-enzyme complex.

Potassium flux in juvenile striped bass (Morone saxatilis): influence of external concentrations of sodium chloride and calcium

Whole-body influx and efflux of K(+) were determined for 25-day-old striped bass,Morone saxatilis, in conditions that simulated harvesting fish from ponds. During the first 5h in fresh water with combined high NaCl (80 mM) and low Ca(2+) (0.12 mM) concentrations, a combination that is acutely lethal to this age of striped bass, K(+) influx for fish in 0.07 mM K(+) was 21±1.7 (SEM) compared to 3.4±0.33 nmol g(-1) h(-1) for fish in water with low Na(+) (0.25 mM) or high Ca(2+) (2.5 mM) concentrations. Influx of K(+) was inhibited during the first few hours after fish were placed in flux chambers. Potassium efflux as percentage of(42)K lost per hour was two-fold higher from fish in the high Na-low Ca treatment compared to fish in low concentrations of Na(+) or high concentrations of Ca(2+). Potassium efflux was probably much greater than influx, but exact values for efflux could not be calculated from the data available. Survival of fish in water with high Na-low Ca was not increased by addition of KCl to the water, indicating that the net loss of K(+) was probably not the cause of death.

Effects of sodium concentration on human neutrophil bactericidal functions

What are the ionic requirements for neutrophil (PMN) function and how might altered electrolyte concentrations contribute to airway disease? The in vitro killing of Pseudomonas aeruginosa by human peripheral white blood cells (WBCs) was progressively compromised Na+ concentration was lowered from 124 to 62 mM; at 62 mM Na+, bactericidal activity was 28.8 +/- 7.4% (SE) of normal. In contrast, Cl- concentration affected killing only when lowered to 8 mM. We examined phagocytosis and oxidative metabolism in response to P. aeruginosa or particles opsonized with either immunoglobulin G (IgG) or complement (C'). Phagocytosis of P. aeruginosa and of IgG-coated particles was Na(+)-dependent (31.2 +/- 3.1 and 58.6 +/- 14.2% of normal, respectively, at 62 mM Na+). However, no effect on uptake of C'-coated particles was observed, and the respiratory burst at 70 mM Na+ was normal regardless of stimuli. Thus low Na+ concentration compromises select PMN functions. These results may help explain why airways of cystic fibrosis (CF) patients become colonized with bacteria such as P. aeruginosa. Perhaps the low concentration of Na+ reported for some CF respiratory secretions inhibits bactericidal functions of PMNs, predisposing these patients to airway infections.

Picosecond Photoluminescence Studies of Photocorrosion and Passivation of n-GaAs in Na2S-Containing Solutions

Passivation of n-GaAs by Na{sub 2}S in an electrochemical cell has been studied using photoluminescence decays and voltage dependence of photoluminescence intensity. A significant increase in the degree of passivation of the (100) n-GaAs surface is seen when the concentration of Na{sub 2}S is increased above approximately1 M. The observed passivation in higher concentrations of Na{sub 2}S eventually deteriorates with extended exposure to light. The corrosion that develops when the n-GaAs is in higher concentrations of Na{sub 2}S leads to traps that can be occupied at all voltages. This behavior is different from corrosion seen in lower concentrations of Na{sub 2}S in which the traps can only be occupied at voltages greater than V = 0.0 V. Decay measurements at flatband potential and at open circuit indicate no significant changes in surface-trapping velocity as the Na{sub 2}S concentration is changed from 0.008 to 1 M. This suggests that repinning or removal of surface traps is not responsible for the passivation that is observed upon increasing the Na{sub 2}S concentration. An increase in the rate of charge transfer across the interface as the Na{sub 2}S concentration in the electrolyte is increased appears responsible. 24 refs., 7 figs., 3 tabs.

Leaf, stolon and root growth of white clover (Trifolium repens L.) in response to irrigation with saline water

The effect of irrigation with water at salinity concentrations of 2.6 and 5.2 dS m−1 on the growth of pure swards of six cultivars of white clover (Trifolium repens L.) was examined over three irrigation seasons at Tatura, Victoria, Australia. After two irrigation seasons, soil EC e levels increased to 6 dS m−1 at 0–60 cm depth in the higher salinity treatment resulting in highly significant (p < 0.001) reductions in shoot dry matter production, flowering densities and petiole and stolon densities. These saline conditions also increased (p <0.001) concentrations of Cl and Na in the shoots and reduced (p < 0.001) leaf water potentials and canopy photosynthetic efficiency rates especially at high temperatures. In contrast, root growth increased at shallow depths (0–15 cm) under both saline irrigation treatments (p <0.001). Cultivars differed significantly in salt tolerance (p < 0.001), with cultivars Haifa and Irrigation exhibiting superior tolerance in terms of lower reductions in herbage yield (p <0.05) and petiole densities (p <0.001) during one irrigation season and lower concentrations of Na and Cl in the shoots (p <0.05) compared with the other four cultivars (Aran, Kopu, Pitau and Tamar). In addition, canopy photosynthetic efficiency rates (A *) in plots irrigated with water at 5.2 dS m−1 were higher in cultivar Haifa compared with cultivar Tamar (p <0.05). The salt tolerance ranking obtained for the six cultivars was in broad agreement with earlier greenhouse studies. Consequently, it appears that, while white clover is an extremely salt-sensitive species, it is possible to grow cultivars which display greater salt tolerance than other cultivars and which provide some scope to increase, or at least to maintain, pasture yields in areas where the soil salinity is low to moderate or where pumped saline groundwater is re-used for Irrigation.

Interplay between sugar and salt on blood pressure in spontaneously hypertensive rats.

Previous experience showed that sucrose ingestion exceeding 50% of total calories consistently increased systolic blood pressure (SBP) in rats, but ingesting 36 or 13% of calories as sucrose did not. In fact, the mean SBP of rats ingesting 36% of calories as sucrose was not different from rats ingesting 13% of calories as sucrose. This was not the case in the present study where the dietary salt content was increased. Adding dietary salt (NaCl) to raise low concentrations of Na (0.14% wt/wt) to higher concentrations (0.80% wt/wt) in diets with 36 and 13% of calories from sucrose significantly elevated SBP in spontaneously hypertensive rats eating both diets, but significantly more in the former. Accordingly, an interplay exists between sugar and salt in SBP regulation, and it is suggested that amounts of sugar characteristically consumed by an average human are capable of increasing BP. Composition of diets, especially with respect to sugar and salt, should be considered when interpreting results from studies on various aspects of hypertension.

Modifications by Na + and K +, and the site of Ag + inhibition in the Na +-translocating NADH-quinone reductase from a marine Vibrio alginolyticus

Modifications by monovalent cations and the site of Ag + inhibition in the Na +-translocating NADH-quinone reductase from a marine Vibrio alginolyticus were examined by kinetic methods using a purified β-subunit and a whole αβγ-complex. The activity of FAD-containing β-subunit for 2-methyl-1,4-naphthoquinone (menadione) and ubiquinone-1 (Q-1) was stimulated by either Na + or K + due to the decrease in K m, which was saturated at about 200 mM. The β-subunit in the complex, however, was already in a state of high-affinity for these quinones, even in the absence of salts, and the activity was further stimulated by either Na + or K +, due to the increase in maximum velocity, which was saturated at about 200 mM. The formation of ubiquinol-1 from Q-1 catalyzed by the complex was not fully activated by K + alone and specifically required Na + for maximum activation. Since the requirement for Na + was greatly decreased in the presence of 200 mM K +, the Na +-dependent reaction catalyzed by FMN-containing α-subunit was saturated by low concentrations of Na + when the β-subunit was in a activated state. Ag +, a specific inhibitor of this enzyme, was found to act as a competitive inhibitor for quinones at the active site of the β-subunit. Since the K i for Ag + (2 nM) was extraordinarily lower than the K m for menadione (15 μM), Ag + was considered to be useful as a specific reagent for the analysis of the active site of the β-subunit.

Refractory inclusions from the Leoville, Efremovka, and Vigarano c3v chondrites: Major element differences between types A and B, and extraordinary refractory siderophile element compositions

We have measured the bulk major and trace element compositions often CAIs from Leoville, Efremovka, and Vigarano, members of the reduced subgroup of C3V chondrites, by INAA. Like CAIs from the reduced subgroup studied previously and unlike CAIs from Allende, a member of the oxidized subgroup, nine of the ten CAIs studied here possess only small amounts of secondary phases and, hence, preserve their pre-alteration bulk major element compositions. Using those compositions and model pre-alteration compositions of Allende CAIs, we cannot distinguish Type B1s clearly from B2s, nor some CTAs from FTAs. All Type As and most Type Bs have superchondritic CaO Al 2O 3 ratios, suggesting that their precursors condensed from a solar gas after ~20% of the Al was removed by high-temperature, Al-rich phases. Type Bs possess higher concentrations of MgO and SiO 2 than do Type As because the precursor phases of Type Bs reacted with the cooling nebular gas to form fassaite, while those of Type As did not. Eight of the ten CAIs have unusual or unique refractory trace element characteristics compared to those seen in Allende inclusions. Vig1, L2, Ef1, and Ef2 have remarkably high concentrations of Re and Os (~57–145 × Cl) because they sampled 4–9 times more hcp condensate metal alloy than did most Allende inclusions. Vig1, L2, Ef1, Ef2, L1, and Vig2 have unusually large Os Ru ratios (up to 6.9 × Cl) because the removal temperatures of their hcp alloy precursors were unusually high (up to ~ 1655 K at 10 −3atm). L2 and L4 have low Zr Hf ratios (~0.4 × Cl); L1 and Ef2, low V/Yb ratios (~0.25 × Cl); Ef2, high Th La (~1.6 × Cl), and Sr Yb (~-2.4 × Cl) ratios; and ED, high Hf Lu (~2.6 × Cl), Sc Lu (~3.1 × Cl), and Zr Lu (~2.8 × Cl) ratios. Most of these fractionations are explained by non-representative nebular sampling of one or more of hibonite, zirconium oxide, perovskite, and melilite, which may be condensates or evaporation residues. Of twenty-five inclusions from the reduced subgroup now studied in this laboratory, seventeen have at least one pair of refractory trace elements which are more fractionated relative to one another compared to Cl chondrites than are the same elements in Allende CAIs, indicating that the host phases of these elements were not as thoroughly mixed together in the nebular region where CAIs of the reduced subgroup accreted as where those in Allende did. Parts of the nebula sampled by C3V chondrites of the reduced subgroup were not well sampled by Allende, and vice versa. Like most coarse-grained inclusions from the reduced subgroup studied previously, most of those analyzed here have lower concentrations of Na, Au, Fe, Zn, and Mn than their Allende counterparts, consistent with the idea that they experienced secondary alteration at a higher temperature or for a shorter time than did Allende inclusions.

Na+ responses of two marine bacteria that did not appear to require Na+ for growth

Two Gram-negative heterotrophic marine bacterial strains had been reported not to require Na+ when grown on a chemically defined medium solidifed with purified agar and prepared without added Na+. When these strains were tested in a chemically defined liquid medium they required at least 3 mM Na + for growth. The agar used in the plating medium was found to contribute 3.3 mM Na+. Increasing the concentrations of Na+ in the liquid medium above 3 mM increased the rate and extent of growth of both organisms and decreased the lag periods. Optimal Na+ concentrations for growth varied from 100 to 500 mM depending on the organism and the carbon source in the medium. Na+ was also required for the transport of the carbon source into the cells. For the maximal rate of transport of L-glutamate, one organism required only 10 mM Na +, the other, 50 mM. For acetate and succinate transport the optimal Na+ concentrations varied from 30 to 200 mM depending on the substrate and the organism. When the initial rate of transport of glutamate into one of the organisms was plotted against Na+ concentration the reponse curve was sigmoid and a Hill plot of the data indicated that the transport protein may possess three binding sites for Na+. Evidence was obtained indicating that both organisms possess a Na+-stimulated NADH oxidase. The results indicate that there are marine bacteria that grow to a limited extent at appreciably lower concentrations of Na+ than have been realized previously and for these a much more definitive examination of the requirement for Na+ is necessary.Key words: marine bacteria, Na+ requirement, growth, membrane transport, NADH oxidase.