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PubMed1997

Characterization and regulation of taurine transport in Caco-2, human intestinal cells.

We characterized the taurine transport system in human intestinal Caco-2 cells and showed that it is subject to adaptive regulation. The activity of taurine transport in Caco-2 cells was evaluated by means of an Na+- and Cl(-)-dependent high-affinity transport system, the characteristics of which were similar to those of the beta-amino acid-specific taurine transport system previously described for various tissues. The activity of taurine transport was down-regulated on culturing in taurine-containing medium. This taurine-induced down-regulation was dependent on both the incubation time with taurine and the concentration of taurine. Hypotaurine and beta-alanine were also capable of inducing this adaptive regulation, whereas alpha-amino acids and gamma-aminoisobutyric acid were not. Kinetic analysis of control and taurine-treated cells suggested that the down-regulation was associated with a decrease in the maximal velocity of taurine transport and also with a decrease in the affinity of the taurine transporter. Cycloheximide treatment weakened the taurine-induced down-regulation. The mRNA level of the taurine transporter (HTAU type) in taurine-treated cells was markedly decreased compared with in control cells. These results indicate that a complex regulatory mechanism is involved in this down-regulation.

Adaptation, Physiological↗
PubMed1982

Purification and properties of beta-alanine aminotransferase from rabbit liver.

beta-Alanine aminotransferase from rabbit liver has been purified 1,700-fold over the initial liver extract. The purified enzyme was shown to be homogeneous by disc electrophoresis and SDS polyacrylamide electrophoresis. The molecular weight of the purified enzyme determined by gel filtration was 95,000 +/- 5,700 and the subunit molecular weight was 48,000 +/- 2,100. The enzyme showed absorption maxima at 282, 330, and 414 nm and contained only 1 mol of pyridoxal 5'-phosphate/mol of dimer. The pH optimum for enzyme activity was 8.8 and the Km values for beta-alanine and 2-oxoglutaric acid were calculated to be 3.9 and 1.4 mM, respectively. The enzyme catalyzed transamination of various omega-amino acids with 2-oxoglutaric acid, which was a favourable amino acceptor. beta-Alanine, gamma-aminobutyric acid, and beta-aminoisobutyric acid, which are naturally occurring substrates, were preferred amino donors, but taurine, alanine, ornithine, spermine, and spermidine were not. 6-Azauracil inhibited the enzyme activity with a Ki of approximately 1.5 mM. From the above properties, beta-alanine aminotransferase from rabbit liver was seen to closely resemble with 4-aminobutyrate aminotransferase from liver and brain.

4-Aminobutyrate Transaminase↗
PubMed1978

Membrane transport of sugars and amino acids in isolated protoplasts.

A method has been developed for observing membrane transport in isolated protoplasts. Transport of sugars and amino acids has been studied in protoplasts isolated from the mesophyll of Pisum sativum L. That uptake was not due to passive diffusion through damaged membranes was demonstrated by supplying simultaneously two sugar stereoisomers, the one (3)H-labeled and the other (14)C-labeled. The protoplast membranes were sufficiently functional to discriminate strongly between these stereoisomers.To characterize transport the nonmetabolized glucose analogue 3-O-methyl glucose (MeG) and amino acid analogue alpha-aminoisobutyric acid (AIB) were employed. When uptake was compared per unit of protein as between leaf strips and protoplasts prepared from the same tissue, it was estimated that the protoplasts had retained approximately 40 to 50% of the uptake ability of the whole cells. Uptake of neither MeG nor AIB by protoplasts was linear with time, but the tendency to flatten was more marked for AIB. Addition of Mg-ATP to buffered medium significantly promoted AIB uptake, an effect not ascribable to either chelation or pH. Transport of both MeG and AIB was markedly pH-dependent, uptake falling with rise in pH.The stimulatory effect of Mg-ATP and the pH dependence confirm that uptake was not due to a diffusional inward "leak" but involved membrane function.This work demonstrates the feasibility of using isolated protoplasts for membrane transport studies. The potential advantages of using protoplasts for such studies are pointed out.

Journal Article↗
PubMed1978

Evidence for amino Acid-h co-transport in oat coleoptiles.

Microelectrode and tracer techniques were used to test for possible amino acid-H(+) co-transport in coleoptiles of Avena sativa L. cv. "Garry." The amino acid analogue alpha-aminoisobutyric acid (AIB) caused transient depolarization of the membrane potential. The absolute magnitude of the maximum depolarization was affected by the same factors that affected AIB transport. Both increased with higher concentrations of AIB, increased with higher acidities in the medium, and were enhanced by indoleacetic acid (which hyperpolarized the membrane potential). AIB transport was reduced as K(+) concentrations in the medium were increased and by the metabolic inhibitor NaN(3), both of which reduce membrane potentials. Our data fit an amino acid-H(+) co-transport model in which transport is controlled by both the membrane potential and proton concentration components of the chemical potential difference of protons across the coleoptile cell membrane.

Journal Article↗
PubMed1981

Inhibition of the Conversion of 1-Aminocyclopropane-1-carboxylic Acid to Ethylene by Structural Analogs, Inhibitors of Electron Transfer, Uncouplers of Oxidative Phosphorylation, and Free Radical Scavengers.

Cyclopropane carboxylic acid (CCA) at 1 to 5 millimolar, unlike related cyclopropane ring analogs of 1-aminocyclopropane-1-carboxylic acid (ACC) which were virtually ineffective, inhibited C(2)H(4) production, and this inhibition was nullified by ACC. Inhibition by CCA is not competitive with ACC since there is a decline, rather than an increase, in native endogenous ACC in the presence of CCA. Similarly, short-chain organic acids from acetic to butyric acid and alpha-aminoisobutyric acid inhibited C(2)H(4) production at 1 to 5 millimolar and lowered endogenous ACC levels. These inhibitions, like that of CCA, were overcome with ACC. Inhibitors of electron transfer and oxidative phosphorylation effectively inhibited ACC conversion to C(2)H(4) in pea and apple tissues. The most potent inhibitors were 2,4-dinitrophenol (DNP) and carbonyl cyanide m-chlorophenylhydrazone (CCCP) which virtually eliminated ACC-stimulated C(2)H(4) production in both tissues. Still other inhibitors of the conversion of ACC to C(2)H(4) were putative free radical scavengers which reduced chemiluminescence in the free radical-activated luminol reaction. These inhibitor studies suggest the involvement of a free radical in the reaction sequence which converts ACC to C(2)H(4). Additionally, the potent inhibition of this reaction by uncouplers of oxidative phosphorylation (DNP and CCCP) suggest the involvement of ATP or the necessity for an intact membrane for C(2)H(4) production from ACC. In the latter case, CCCP may be acting as a proton ionophore to destroy the membrane integrity necessary for C(2)H(4) production.

Journal Article↗
PubMed1991

Tricholongins BI and BII, 19-residue peptaibols from Trichoderma longibrachiatum. Solution structure from two-dimensional NMR spectroscopy.

Two nonadecapeptides, tricholongins BI and BII, which display antifungal and antibacterial activities, have been isolated from in vitro cultures of the fungus Trichoderma longibrachiatum. The peptides were separated by reversed-phase HPLC; their amino acid compositions were determined by gas chromatography and their sequences by positive-ion fast-atom-bombardment mass spectrometry and high-field NMR. These linear peptides, containing mainly hydrophobic L-amino acids, 8-9 2-aminoisobutyric acid residues and exhibiting an acetylated N-terminal residue and an amino alcohol C-terminal leucinol belong to the peptaibol class. The methanol solution structure of tricholongins BI and BII has been investigated using both one- and two-dimensional NMR techniques. The total 1H-NMR and 13C-NMR assignments are given. By a combination of the 3JNH,C alpha H coupling constant values, temperature coefficients of the NH and CO groups, amide hydrogen/deuterium-exchange rate measurements and NOE data, a secondary structure for tricholongins in solution has been proposed. Both peptides adopt a similar alpha-helical conformation with a hinge around Pro13 resulting from two 3(10) bonds. The results suggest that the N-terminus contains mixed alpha/3(10) bonds. The membrane permeability modifications induced by tricholongins have been assayed by the use of liposomes composed of egg phosphatidylcholine with 20-30% cholesterol. The peptide-induced leakage of an entrapped fluorescent probe has been followed by fluorescence spectroscopy. In a concentration range of 0.13-0.31 microM, tricholongins induce the leakage of 50% of the entrapped material in 20 min.

Amino Acid Sequence↗
PubMed1981

Staphylococcal enterotoxins fail to disrupt membrane integrity or synthetic functions of Henle 407 intestinal cells.

The potential cytotoxic activity of purified staphylococcal enterotoxins for mammalian cells was evaluated. The effects of staphylococcal enterotoxins A (SEA) and B (SEB) on cell membrane integrity as measured by leakage of labeled cytoplasmic constituents ([3H]uridine), amino acid transport (lysine and aminoisobutyric acid), and macromolecular synthesis (protein, ribonucleic acid, and deoxyribonucleic acid) was evaluated for a human intestinal epithelial cell (Henle 407). No evidence of cytotoxicity by any of these criteria could be detected for cell monolayers incubated with SEA for periods of between 30 min and 24 h. Purified staphylococcal hemolysins (alpha- and delta-toxins) were shown to exert cytotoxicity by the leakage and amino acid uptake assays. In efforts to detect synergistic effects between enterotoxin and the staphylococcal cytotoxins, membrane functions were evaluated after sequential or combined treatment with enterotoxin and alpha-toxin or with enterotoxin and delta-toxin. In no instance could a contribution to cytotoxicity by the staphylococcal enterotoxin be detected. That the assays were sufficiently sensitive to detect synergistic effects was shown by the greater than additive effects achieved with a combination of alpha- and delta-toxins. The data, contrary to previous reports, showed that staphylococcal enterotoxins did not behave as bacterial cytotoxins.

Animals↗
PubMed1986

Differences in function and structure of the capillary endothelium in the supraoptic nucleus and pituitary neural lobe of rats. Evidence for the supraoptic nucleus as an osmometer.

The physiology and structure of capillary endothelial cells in the hypothalamic ventromedial and supraoptic nuclei and pituitary neural lobe were evaluated with quantitative methods and compared. The capillary endothelial cells in the ventromedial nucleus were used as an index of blood-brain barrier endothelium in cerebral gray matter; this endothelium has relatively low surface area and low permeability to tracer solutes. The permeability X surface area product of endothelial cells for a neutral amino acid, 14C-alpha-aminoisobutyric acid (AIB), in the ventromedial nucleus was similar to the value for supraoptic nucleus and was several hundred times smaller than in the neural lobe. The supraoptic nuclei and neural lobe had exceptionally large capillary surface areas, but dissimilar rates of blood flow and transendothelial influx of AIB. Differences in permeability of the endothelial cells between these two structures correlated closely with their marked dissimilarities in morphology. The neural lobe endothelium had numerous fenestrations (five per capillary cross-section) and vesicular profiles (twice as many as supraoptic nucleus), two features commonly associated with high capillary permeability. The capillary endothelium of the supraoptic nucleus was that of a typical blood-brain barrier structure having intercellular junctions that appeared tight, no fenestrations, and few cytoplasmic pits and vesicles. The unusually large capillary surface area of the supraoptic nucleus and low rate of solute flux across its endothelial cells make this nucleus a unique structure in which rapid changes in tissue volume may occur in response to small perturbations in plasma osmolality. The findings implicate the supraoptic nucleus as an osmotically sensitive detector or 'osmometer' in neuroendocrine regulation of body fluid homeostasis.

Animals↗
PubMed1986

Differences in function and structure of the capillary endothelium in gray matter, white matter and a circumventricular organ of rat brain.

Physiological and morphometric studies were conducted on the microvascular endothelium of four individual cerebral structures having different neural activities--the inferior colliculus, sensorimotor cortex (both gray matter regions), genu of the corpus callosum (white matter), and the subfornical organ (a circumventricular organ) of rats. The physiological data, obtained by quantitative autoradiography, produced new findings: the rate of blood-to-tissue flux across capillary endothelial cells of a neutral amino acid, 14C-alpha-aminoisobutyric acid, was 100-400 X more rapid in the subfornical organ than in gray and white matter regions, and the transit time of labeled albumin in the subfornical organ microcirculation was 7-12 X longer than in the blood-brain barrier regions. These quantitative studies suggest that circulating messengers, such as hormones, would have more prolonged receptor contact with capillary endothelial cells and greater rates of transendothelial passage in the subfornical organ than in gray or white matter. Capillary densities, volume fractions, and surface areas were similar for the inferior colliculus (which has the highest rates of tissue glucose metabolism and blood flow among blood-brain barrier regions) and the subfornical organ, but were significantly smaller for sensorimotor cortex and corpus callosum (about 35 and 70% lower, respectively). Electron microscopic morphometry of capillary endothelial cells in the inferior colliculus and corpus callosum indicated the ultrastructural basis of blood-brain barrier mechanisms in these regions--intercellular junctions that appeared tight, few cytoplasmic vesicular profiles, and no fenestrations. Analysis of endothelial cells in the subfornical organ demonstrated 7 X more vesicular profiles and 4 fenestrations per cross section of capillary. These findings represent structural evidence for high rates of solute flux across the capillary endothelium of circumventricular organs.

Animals↗
PubMed1978

Characterization of a carrier-mediated transport system for taurine in the fetal mouse heart in vitro.

Cardiac taurine levels are elevated in hypertension and congestive heart failure. A possible mechanism for this increase in taurine is an alteration of its uptake. We sought to identify and characterize a carrier-mediated transport system for taurine in the mammalian myocardium utilizing the fetal mouse heart in organ culture. Hearts from fetuses of 16-19 days gestational age used in these studies had an endogenous taurine content of 14.1+/-0.5 nmol/mg tissue. The uptake of [(3)H]taurine was linear for up to 8 h. Taurine was accumulated against a concentration gradient as demonstrated by a net increase in taurine concentration when hearts were incubated in 0.5 mM taurine. [(3)H]Taurine uptake was saturable, K(m) = 0.44 mM, temperature dependent, and required sodium. The close structural analogues, hypotaurine and beta-alanine, reduced [(3)H]taurine uptake by 87% when present in 100-fold excess. The alpha-amino acids alanine, alpha-aminoisobutyric acid, glycine, leucine, and threonine did not inhibit uptake. Other taurine analogues tested were guanidinotaurine, guanidinopropionic acid, gamma-aminobutyric acid, 2-aminoethane phosphonic acid, aminomethane sulfonic acid, 3-aminopropane sulfonic acid, N-acetyltaurine, and isethionic acid. We conclude that a carrier-mediated transport system for taurine exists in the fetal mouse heart based on the demonstration of (a) temperature dependence, (b) saturability, and (c) structural selectivity of the uptake process. Transport was demonstrated to be mediated by a beta-amino acid uptake system. In addition, taurine uptake was observed to be sodium dependent, energy dependent, and capable of accumulating taurine against a concentration gradient.

Animals↗
PubMed1984

Biological evaluation of radiolabeled D-methionine as a parent compound in potential nuclear imaging.

Based on the high radioactivity uptake of some 14C-labeled D-amino acids in tumors and pancreas of mice, this investigation was undertaken to ascertain possible usefulness of radioactive D-methionine as a nuclear imaging agent. Radioactivity derived from D-[3,4-14C]-methionine in Ehrlich solid tumor was approximately three times higher than that from the L-isomer, but was the same as for mouse pancreas. Excretion rate of the radioactivity of D-[14C]-methionine into urine was approximately two times faster than that of the L-isomer. As compared with two potential imaging agents, 1-aminocyclopentane-1-carboxylic acid and alpha-aminoisobutyric acid, D-methionine showed almost the same radioactivity biodistribution in tumor and pancreas. These results suggest potential for D-methionine as a mother compound for use in tumor and pancreas imaging.

Animals↗
PubMed2001

Novel fungal metabolites as cell wall active antifungals: fermentation, isolation, physico-chemical properties, structure and biological activity.

Two novel antifungal compounds, 1 (SCH 466457), and 2 (SCH 466456), active in a "cell wall" assay, were isolated from the fermentation broth of an unidentified fungus. The active compounds were separated from the broth filtrate by adsorption on a macroreticular resin and were purified on reverse phase HPLC. Detailed mass spectrometric and NMR experiments and degradative studies helped in elucidating the structures of these compounds. The compounds were identified to be peptides containing amino acids such as alanine, aminoisobutyric acid, proline, leucine, valine, glycine and a previously identified beta-keto acid, 2-methyl 3-oxotetradecanoic acid. (5) Both compounds were active against Candida, dermatophytes and Aspergillus (Geometric Mean MIC's, 8.9, 20 and 16 microg/ml, and 64, 128 and 23 microg/ml, respectively for 1 and 2).

Anti-Bacterial Agents↗
PubMed2003

Novel fungal metabolites as cell wall active antifungals: fermentation, isolation, physico-chemical properties, structure and biological activity.

Two novel antifungals SCH 643432 (1), and 2, were isolated from the fermentation broth of a fungus taxonomically classified as a Paecilomyces varioti. These compounds were separated from the fermentation broth filtrate by adsorption on a macroreticular resin XAD-16 (Amberlite). Purification and separation of the individual compounds were achieved by trituration of the extract with dichloromethane followed by preparative HPLC using reverse phase columns. Extensive FAB (Fast Atom Bombardment) and ESI (Electro Spray) mass spectrometric studies using fragmentation of various daughter ions, NMR experiments and degradative studies helped in elucidating the structure of compound 1. Compound 2 is an isomer of SCH 643432 (1). They were identified as straight chains peptides containing several amino acids such as alanine, aminoisobutyric acid, proline, leucine, glycine and arginine. The N-terminal is terminated in a previously identified beta-keto acid, 2-methyl 3-oxo tetradecanoic acid (MOTDA). Both compounds were active against Candida albicans, other Candidas, dermatophytes and Aspergillus (Geometric Mean MIC's 4.00, 2.59, 3.56, 11.31 and 4.49, 4.00, 5.66, 16.0 microg/ml, respectively for 1 and 2).

Antifungal Agents↗