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PubMed2006

Salting the charged surface: pH and salt dependence of protein G B1 stability.

This study shows significant effects of protein surface charges on stability and these effects are not eliminated by salt screening. The stability for a variant of protein G B1 domain was studied in the pH-range of 1.5-11 at low, 0.15 M, and 2 M salt. The variant has three mutations, T2Q, N8D, and N37D, to guarantee an intact covalent chain at all pH values. The stability of the protein shows distinct pH dependence with the highest stability close to the isoelectric point. The stability is pH-dependent at all three NaCl concentrations, indicating that interactions involving charged residues are important at all three conditions. We find that 2 M salt stabilizes the protein at low pH (protein net charge is +6 and total number of charges is 6) but not at high pH (net charge is or=18). Furthermore, 0.15 M salt slightly decreases the stability of the protein over the pH range. The results show that a net charge of the protein is destabilizing and indicate that proteins contain charges for reasons other than improved stability. Salt seems to reduce the electrostatic contributions to stability under conditions with few total charges, but cannot eliminate electrostatic effects in highly charged systems.

Bacterial Proteins↗
PubMed1996

Unchanged 24 h ambulatory blood pressure during shjort-term salt restriction and salt repletion in normotensive volunteers.

BACKGROUND: The lack of significant correlation between sodium consumption and blood pressure in a population has tentatively been explained by individual differences in salt sensitivity. Previously we have shown that one-third of essential hypertensived patients respond to a salt load of 9 g daily for 5 days with an increase of 10% or more in 24 h ambulatory blood pressure. The present study was undertaken to examine the response to salt loading in healthy normotensive people. RESULTS:Only one out of 17 volunteers (6%) with a mean age of 24 years and mean ambulatory blood pressure of 136/70 mmHg had an increase in mean ambulatory blood pressure of at least 10% during salt loading. On average, blood pressure did not differ during periods of normal (150 mmol/24 h), low (120 mmol/24 h) or high (268 mmol/24 h) sodium excretion, respectively. CONCLUSION: Normotensive people tolerate short-term salt loading without significant changes in 24 h ambulatory blood pressure.

Journal Article↗
PubMed1992

Regulation of intracellular osmotic pressure during the initial stages of salt stress in a salt-tolerant yeast, Zygosaccharomyces rouxii.

The accumulation of glycerol and inorganic ions as it related to osmotic pressure, and the regulation of intracellular osmotic pressure in a salt-tolerant yeast, Zygosaccharomyces rouxii, were examined for several hours after salt stress. Intracellular contents of glycerol increased for up to 6 h in media supplemented with 1 M and 2 M NaCl and did not increase in medium containing 3 M NaCl. Intracellular contents of Na+ and Cl- reached a maximum value within 1 and 3 h, respectively, in all NaCl-containing media and increases were proportional to the concentration of NaCl in the medium. As glycerol was accumulated in cells, the intracellular contents of Na+ and Cl- gradually decreased in media containing 1 M and 2 M NaCl. After salt stress, cell volume decreased within 1 h and the original volume was re-established for 3 to 6 h in media with 1 M and 2 M NaCl but not in medium with 3 M NaCl. Intracellular concentrations of solutes, which were calculated from the total contents of glycerol and inorganic ions and the cell volume, became almost equivalent to the external osmotic pressure within 1 h after salt stress. Experiments using various inhibitors showed that a large amount of ATP was required not only for the synthesis and accumulation of glycerol but also for the exclusion of Na+ and Cl- from cells under salt-stressed conditions.

Culture Media↗
PubMed1986

Atrial natriuretic factor in inbred Dahl salt-sensitive and salt-resistant rats.

The atria of adult Dahl salt-sensitive (S) rats contain more atrial natriuretic factor (ANF) than the atria of adult Dahl salt-resistant (R) rats by both radio-immunoassay and bioassay. This strain difference is not present between 1 and 15 days of age but is present at 30 days of age and persists throughout adulthood. The precursors of ANF immunoprecipitated from in vitro translations of atrial messenger RNA (mRNA) had the same molecular weight in S and R strains. Hypothalamic levels of ANF were similar in S and R. Kidneys of weanling S rats were hyporesponsive to ANF compared with R, but as the S rats became hypertensive with age the situation was reversed, with S rats being hyperresponsive to ANF. Aortic vascular responses to ANF were identical in S and R rats. Plasma ANF was similar in S and R rats on low-salt diet, but increased markedly in S, but not R, on high-salt diet. It is concluded that any genetic defect in the ANF system in Dahl S rats is most likely to involve the kidney response to ANF, and that high plasma ANF in salt-fed rats may be a consequence of volume expansion and hypertension.

Animals↗
PubMed1994

Mechanisms of the natriuretic effects of neutral endopeptidase inhibition in Dahl salt-sensitive and salt-resistant rats.

To explore the mechanisms of the renal effects of neutral endopeptidase (NEP) inhibition, the effects of an NEP inhibitor, candoxatril (UK 79,300; UK), in Dahl salt-sensitive (SS) and salt-resistant (SR) rats were examined. UK dose-dependently decreased blood pressure (BP) in SS rats (20 mg/kg: 174 +/- 5 vs. 155 +/- 8 mm Hg, p < 0.01) but not in SR rats. Urinary sodium excretion (UNaV) of both rat strains receiving high-salt diets was increased to a greater extent than that of rats receiving low-salt diets. Basal plasma atrial natriuretic peptide (ANP) level in hypertensive SS rats was higher than in SR rats (192 +/- 18 vs. 118 +/- 24 pg/ml, p < 0.05). UK increased ANP levels in the plasma and urine two- and 11-fold, respectively. UK-induced increases in UNaV, urinary cyclic GMP, and plasma ANP concentrations were significantly augmented by coadministration of a clearance receptor agonist, C-ANF(4-23) or brain natriuretic peptide (BNP). Thus, the effects of NEP inhibition appear to be potentiated by the reduced receptor-mediated metabolism of ANP. This may explain the greater response to the NEP inhibitor in Dahl rats with hypertension or high-salt feeding.

Animals↗
PubMed1996

TGF and nitric oxide: effects of salt intake and salt-sensitive hypertension.

The tubuloglomerular feedback response (TGF) entails vasoconstriction of the afferent arteriole (AA) and a fall in the glomerular capillary pressure (PGC) and single nephron glomerular filtration rate (SNGFR) during NaCl reabsorption in the macula densa (MD) segment. Recent studies have concluded that nitric oxide (NO) is synthesized by the MD and blunts the TGF response. Since a high salt (HS) diet has been found to blunt TGF, we tested the effects of salt intake on the response to blockade of nitric oxide synthesis. For the first series, the TGF was assessed from changes in proximal stop-flow pressure (PSF, an index of PGC in response to graded perfusion of the loop of Henle (LH) with name tubular fluid (NTF). Loop perfusion with 10(-3) M L-NMA did not affect the PSF responses of low salt (LS) rats, but reduced (P < 0.01) the PSF of HS rats during perfusion at 20 nl.min-1 (-1.5 +/- 0.4 mm Hg; P < 0.01) and at 40 nl.ml-1 (-2.2 +/- 0.5 mm Hg; P < 0.001). For the second series, the TGF responses of salt sensitive Dahl/Rapp (ssDR) rats were compared to Sprague-Dawley (SD) rats. Both groups were studied 8 to 10 days after starting HS or LS diets by loop perfusion of artificial tubular fluid at 40 nl.min-1. Compared to Sprague-Dawley rats, the ssDR had blunted maximal TGF responses during LS (SD, 8.2 +/- 0.3 vs. ssDR, 6.4 +/- 0.3 mm Hg; P < 0.001), but not during HS. During LS intake, addition of L-NMA to ATF perfusing the loop of Henle did not alter the maximal TGF response of either strain. However, during HS intake L-NMA increased the maximal TGF response of SD rats (4.4 +/- 0.4 to 6.7 +/- 0.5 mm Hg; P < 0.001) but did not significantly change the PSF of ssDR rats (5.2 +/- 0.3 to 5.7 +/- 0.5 mm Hg; NS). We conclude that the TGF response is enhanced by blockade of NOS during HS, but not LS intakes; this response to NOS blockade during HS intake is lost in salt sensitive Dahl/Rapp rats.

Animals↗
PubMed1998

Enhanced Na+-dependent bile salt uptake by WIF-B cells, a rat hepatoma hybrid cell line, following growth in the presence of a physiological bile salt.

Although bile salts are toxic to the liver at high plasma concentrations, the effects of physiological concentrations of bile salts on normal hepatic function are poorly understood. We examined the effect of taurocholate (TC) on the basolateral uptake of [3H]TC in WIF-B cells, a hybrid cell line stably exhibiting in vitro the structural and functional polarity of hepatocytes. Cells were grown in the absence or presence of TC (50 micromol/L) over 12 days, and then incubated with [3H]TC concentrations ranging from 1 to 250 micromol/L. For both control and TC-grown cells, uptake of [3H]TC was linear over 2 minutes. In control cells, the Km for [3H]TC Na+-dependent uptake over 1 minute was 6 +/- 5 micromol/L, and the Vmax was 45 +/- 6 pmol TC/mg protein/min (+/- SEM). TC-grown cells exhibited no significant change in Km but showed a doubling of Vmax to 87 +/- 6 pmol TC/mg protein/min (P < .005). In both control and TC-grown cells, maximal uptake of [3H]TC occurred following 10 to 12 days in culture, with TC-grown cells consistently showing greater rates of [3H]TC uptake from 4 to 14 days in culture. Western blots immunostained for the basolateral Na+-dependent plasma membrane protein, ntcp, revealed the appropriate approximately 50-kd band in control and TC-grown cells, and confocal immunofluorescence microscopy demonstrated staining along the basolateral plasma membrane. Northern blots hybridized with a cDNA probe directed against ntcp indicated a modest TC-induced increase in mRNA levels. Reverse-transcriptase polymerase chain reaction (RT-PCR) using RNA isolated from WIF-B cells and oligonucleotide primers specific for rat ntcp or human NTCP transcripts revealed only the presence of the rat ntcp transcript. We conclude that bile salts, at concentrations normally found in mammalian portal blood, may be capable of promoting enhanced hepatocellular bile salt uptake via an increase in basolateral Na+-dependent plasma membrane transport capacity.

Animals↗
PubMed1992

A novel and conserved salt-induced protein is an important determinant of salt tolerance in yeast.

We have isolated a novel yeast gene, HAL1, which upon overexpression improves growth under salt stress. In addition, disruption of this gene decreases salt tolerance. Therefore HAL1 constitutes a rate-limiting determinant for halotolerance. It encodes a polar protein of 32 kDa located in the yeast cytoplasm and unrelated to sequences in data banks. The expression of this gene is increased by high concentrations of either NaCl, KCl or sorbitol. On the other hand, the growth advantage obtained by overexpression of HAL1 is specific for NaCl stress. In cells overexpressing HAL1, sodium toxicity seems to be counteracted by an increased accumulation of potassium. The HAL1 protein could interact with the transport systems which determine intracellular K+ homeostasis. The HAL1 gene and encoded protein are conserved in plants, being induced in these organisms by salt stress and abscisic acid. These results suggest that yeast serves as a convenient model system for the molecular biology of plant salt tolerance.

Amino Acid Sequence↗
PubMed1987

Synergism of organic zinc salts and sulfhydryl compounds (thiols) in the protection of mice against acute ethanol toxicity, and protective effects of various metal salts.

Organic zinc salts such as zinc aspartate, zinc orotate, zinc histidine and zinc acetate protected mice against the lethality of an acute intraperitoneal challenge with ethanol. A similar activity was also provided by salts of cobalt, zirconium, lithium and magnesium. Organic zinc salts acted synergistically with sulfhydryl compounds in protecting the mice and potentiation between the two categories of agents was seen. The results are in analogy to radioprotective effects by zinc and thiols and imply that organic zinc salts may, alone or in conjunction with thiols, reduce in a wider context tissue injury caused by free radical-mediated mechanisms.

Alcoholic Intoxication↗
PubMed1985

Influence of microbial bile salt desulfation upon the fecal excretion of bile salts in gnotobiotic rats.

The fecal excretion of intraperitoneally injected 24-14C-labeled taurocholate (TCA), taurolithocholate (TLCA) and the respective 3-sulfate esters (TCA-3-S; TLCA-3-S), were compared in germfree (GF) rats, conventional (CV) rats, and in gnotobiotic rats associated with Clostridium Cl-8 or this same strain Cl-8 plus the bile desulfating Clostridium S1, respectively. TCA and TLCA were about two times more rapidly excreted by CV animals than by GF animals; the time required for 50% excretion of total label injected (t 1/2) was 6.6 days vs 14.9 for TCA, and 4.4 vs 8.9 for TLCA. In GF and in CV animals, TCA-3-S and TLCA-3-S were excreted more rapidly than their nonsulfated analogues; the t 1/2 values of TCA-3-S and TCA were 2.7 days vs 14.9 in GF rats, and 3.1 vs 6.6 days in CV animals. The t 1/2 values of TLCA-3-S and TLCA were 2.7 days vs 8.9 in GF rats, and 1.5 vs 4.4 days in CV rats. In gnotobiotic rats associated with Clostridium strains S1 + Cl-8, fecal bile salts were nearly 100% deconjugated and desulfated and the 50% excretion times of TCA-3-S and TLCA-3-S approximated to those of TCA and TLCA in GF animals. T 1/2 of TCA-3-S in gnotobiotic S1 + Cl-8 animals was 12.2 days vs 14.9 for TCA in GF animals. In gnotobiotic S1 + Cl-8 animals the t 1/2 of TLCA and TLCA-3-S was 12.5 and 11.0 days, respectively. These results illustrate clearly the important effect the intestinal microflora has upon the metabolic half-life of bile salts. Moreover, they demonstrate that desulfation of bile salts by the intestinal microflora takes place in intestinal segments from where a certain degree of reabsorption is still possible, and thus point to the fact that microbial desulfation is an important variable in the overall elimination of bile salts.

Animals↗
PubMed1991

Rat taste nerve responses to salts carrying cations of large molecular size; are the taste responses to the salts induced by cation transport across apical membranes of taste cells?

1. The responses of rat chorda tympani nerve to various salts carrying cations of large molecular size which have small permeability were measured. 2. Salts carrying polyvalent cations such as Fe3+ or La3+ elicited much larger responses than NaCl or KCl. 3. Ammonium chloride derivatives having methyl or ethyl groups and salts carrying other organic cations of large molecular size elicited the responses comparable to that induced by NH4Cl or NaCl. 4. It was suggested that the taste responses to the salts carrying the cations of large molecular size are induced not by the cation transport but by adsorption of the cations on the membranes.

Animals↗
PubMed2004

Effect of the adaptation to high bile salts concentrations on glycosidic activity, survival at low PH and cross-resistance to bile salts in Bifidobacterium.

Six derivatives with increased resistance to ox gall (MIC: > or = 1% w/v) and one derivative resistant to sodium cholate (MIC: 0.8% w/v) were obtained from more sensitive original Bifidobacterium strains. These microorganisms, and two additional cholate resistant derivatives obtained in a previous study (Int. J. Food Microbiol. 82 (2003) 191), were partially characterised in this study. Acquisition of resistance against a given bile salt, also conferred cross-resistance to other bile salts, and promoted an increase in the survival of these microorganisms at low pH. Bile resistance levels of derivatives were dependent on the external pH so that the resistance was lower at neutral pH values than in acidic environments. In addition, the acquisition of bile resistance induced changes on glycoside-hydrolysing activities of derivatives obtained from five out of eight original strains, with certain activities such as beta-glucosidase showing more than tenfold increases in some of these microorganisms. These data suggest that the exposure to high bile salts concentrations may have induced a synergic response on Bifidobacterium for the adaptation to the conditions of the gastrointestinal tract. This could have improved the survival at low pH in these microorganisms, the resistance to high bile salts concentrations, and the assimilation of non-digestible carbohydrates by the enhancement of some glycoside-hydrolysing activities.

Adaptation, Physiological↗
PubMed2000

A comparison of the permeation enhancement potential of simple bile salt and mixed bile salt:fatty acid micellar systems using the CaCo-2 cell culture model.

The aim of this study was to compare the permeation enhancing potential and toxicity of simple bile salt and bile salt:fatty acid mixed micellar systems using the CaCo-2 cell culture model. The effects of micellar systems of sodium cholate, (NaC), and sodium taurocholate, (NaTC), on the permeability of the hydrophilic markers, mannitol (182) and polyethylene glycols (PEGS) 900 and 4000, were assessed. Simple micelle systems of the unconjugated bile salt, NaC, caused greater enhancement of the hydrophilic markers than the conjugated bile salt, NaTC. In the case of NaC systems the enhancement was coincident with excess membrane disruption and toxicity as indicated by altered TEERs, TEMs, MTT values, and, the lack of recovery following removal of the enhancer. In contrast, the NaTC systems were less toxic, and, in the simple micelle form the likely mechanism of enhancement of the hydrophilic markers is via a transient effect on the tight junctions. Formation of mixed micellar systems with linoleic acid (LA) accentuated the toxic effects of NaC. In comparison, NaTC:LA mixed micelles showed superior permeability enhancement versus simple micelles without increasing membrane toxicity. The mechanism of enhancement of NaTC:LA appears more complex and involves a possible combination effect on both the paracellular and transcellular routes.

Bile Acids and Salts↗
PubMed1984

The effects of colchicine on secretion into bile of bile salts, phospholipids, cholesterol and plasma membrane enzymes: bile salts are secreted unaccompanied by phospholipids and cholesterol.

Colchicine, a drug which interferes with microtubular function, has no effect on the secretion of taurodehydrocholate into bile; it is therefore suggested that bile salts are unlikely to be packaged in vesicles during cellular transit from sinusoidal to canalicular membranes. Colchicine greatly reduces the secretion of phospholipid and cholesterol into bile; it is suggested that this is due to an interruption in the supply of vesicles bringing lipids to repair the canalicular membrane during bile salt output. In the absence of the protective effect of a continuous supply of repair vesicles, micelleforming bile salts damage the canalicular membrane; the increased concentration of plasma membrane enzymes in bile and the increased aspartate aminotransferase activity in plasma and bile are evidence of this damage. Damage to the canalicular membrane may also be an explanation for the reduction in taurocholate transport and the taurocholate-induced cholestasis which are seen with colchicine-treated livers. Such membrane damage is not observed in colchicine-treated livers during the secretion of the non-micelle forming bile salt, taurodehydrocholate.

Animals↗
PubMed2000

Isolation and characterization of a Lactobacillus amylovorus mutant depleted in conjugated bile salt hydrolase activity: relation between activity and bile salt resistance.

Growth experiments were conducted on Lactobacillus amylovorus DN-112 053 in batch culture, with or without pH regulation. Conjugated bile salt hydrolase (CBSH) activity was examined as a function of culture growth. The CBSH activity increased during growth but its course depended on bile salts type and culture conditions. A Lact. amylovorus mutant was isolated from the wild-type strain of Lact. amylovorus DN-112 053 after mutagenesis with N-methyl-N'-nitro-N-nitrosoguanidine. An agar plate assay was used to detect mutants without CBSH activity. In resting cell experiments, the strain showed reduced activity. Differences between growth parameters determined for wild-type and mutant strains were not detected. Comparative native gel electrophoresis followed by CBSH activity staining demonstrated the loss of proteins harbouring this activity in the mutant. Four protein bands corresponding to CBSH were observed in the wild-type strain but only one was detected in the mutant. The specific growth rate of the mutant strain was affected more by bile salts than the wild-type strain. Nevertheless, bile was more toxic for the wild-type strain. In viability studies in the presence of nutrients, it was demonstrated that glycodeoxycholic acid exerted a higher toxicity than taurodeoxycholic acid in a pH-dependent manner. No difference was apparent between the two strains. In the absence of nutrients, the wild-type strain died after 2 h whereas no effect was observed for the mutant. The de-energization experiments performed using the ionophores nigericin and valinomycin suggested that the chemical potential of protons (ZDeltapH) was involved in Lactobacillus bile salt resistance.

Amidohydrolases↗
PubMed1999

The chimeric peptide [Lys(-2)-Arg(-1)]-sarafotoxin-S6b, composed of the endothelin pro-sequence and sarafotoxin, retains the salt-bridge staple between Arg(-1) and Asp8 previously observed in [Lys(-2)-Arg(-1)]-endothelin. Implications of this salt-bridge in the contractile activity and the oxidative folding reaction.

The chimeric peptide [Lys(-2)-Arg(-1)]-sarafotoxin-S6b (KR-SRTb) designed from the Lys-2-Arg-1 dipeptide of the endothelin pro-sequence and the sarafotoxin-S6b sequence was synthesized. Its contractile activity was found to be decreased markedly when compared with that of the parent SRTb. In contrast, the extension by the Lys-Arg dipeptide was found to increase the formation of the native disulfide isomer (82/18 versus 96/4) when the reaction was carried out in the presence of redox reagents. The solution structure of KR-SRTb was determined by NMR as a function of pH. In the carboxylic acid state, the structure consists of the cystine-stabilized alpha-helical motif, with the alpha-helical part spanning residues 9-15, and of an unstructured C-terminal tail. In the carboxylate state, the structure is characterized by a salt-bridge between Arg(-1) and Asp8, which we identified previously in the [Lys(-2)-Arg(-1)]-endothelin-1 peptide (KR-ET-1). The fact that this salt-bridge is commonly observed in KR-SRTb and KR-ET-1, despite the 33% sequence difference between the corresponding parental peptides, highlights the remarkable adaptability of the Lys-Arg extension for the formation of a special salt-bridge. As a consequence, this salt-bridge, which does not depend on either the 4-7 sequence of the loop or the C-terminal sequence, appears to be particularly well suited to improve the stability of the cystine-stabilized alpha-helical motif. Therefore, because of its high yield in the native disulfide arrangement and its high permissiveness for sequence mutation in the 4-7 loop, such a stabilized cystine-stabilized alpha-helical motif could be a valuable scaffold for the presentation of a library of constrained short peptides.

Amino Acid Sequence↗
PubMed1961

Effects of chronic excess salt feeding. Enhanced hypertensogenic effect of sea salt over sodium chloride.

Female rats were fed diets containing either excess sea salt or excess sodium chloride for periods up to 14 months. The hypertension produced by sea salt was more pronounced than that caused by sodium chloride alone, although the average amount of sodium chloride contained in the sea salt feeding was slightly less. The ions involved in this incremental effect of sea salt were not identified.

Animals↗
PubMed1981

Structure and activity of malate dehydrogenase from the extreme halophilic bacteria of the Dead Sea. 2. Inactivation, dissociation and unfolding at NaCl concentrations below 2 M. Salt, salt concentration and temperature dependence of enzyme stability.

The stability of halophilic malate dehydrogenase increases with increasing salt concentration and with decrease in temperature. Stabilization by various salts, at high salt concentrations, follows the Hofmeister series. The enzyme inactivation rates closely match dissociation of the dimeric enzymes into monomeric subunits and unfolding of the polypeptide chains, as followed by velocity sedimentation, light scattering and circular dichroism measurements. The alpha-helix content goes to zero upon denaturation. Unusual water and salt binding properties of the native enzyme (cf. preceding paper, in this journal) are believed to be largely lost upon enzyme dissociation and unfolding. The properties thus seem to be associated with the intact structure of the enzyme.

Chemical Phenomena↗