Search PubMed⌕ Search

SEARCH · Search PubMed

Results for “AMINOISOBUTYRIC ACID”

Search indexed PubMed citations on genomics, clinical trials, systematic reviews and public health. Explore titles, authors and supplied subject terms, then open the PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 541 records · Page 30Linked to original sources
PubMed1980

Energization of glucose transport by Pseudomonas fluorescens.

We have measured the capacity of Pseudomonas fluorescens to transport the glucose analog 2-deoxy-d-glucose and the amino acids l-alanine and alpha-aminoisobutyric acid under conditions in which the cells could generate (i) both a membrane proton motive force and high-energy phosphate compounds, (ii) a proton motive force but not high-energy phosphate compounds, and (iii) neither a proton motive force nor high-energy phosphate compounds. This was done by depleting cells of adenosine triphosphate stores by treatment with sodium arsenate and then suspending them in a phosphate-free medium, where they could generate a proton motive force but not phosphate bond energy, or in a phosphate-containing medium, where they could generate both a proton motive force and phosphate bond energy. Inclusion of the proton-conducting ionophore carbonyl cyanide-m-chlorophenyl hydrazone under either condition precluded the generation of both a proton motive force and phosphate bond energy. The amino acids l-alanine and alpha-aminoisobutyric acid were transported independently of phosphate bond energy and required only a proton motive force. 2-Deoxy-d-glucose was transported only under conditions in which phosphate bond energy could be generated. These results are consistent with the findings of others that Pseudomonas aeruginosa produces an inducible shock-sensitive glucose-binding protein and conform to the generalization that binding protein-associated transport systems are energized by phosphate bond energy.

Adenosine Triphosphate↗
PubMed1977

3':5'-cyclic AMP: independent induction of amino acid transport by epinephrine in primary cultures of adult rat liver cells.

Liver cells were obtained from adult rats by a collagenase perfusion technique and cultured as monolayers in serum-free media. Epinephrine and isoproterenol both induced large increases in intracellular adenosine 3':5'-monophosphate (cAMP) within 1-2 min whereas epinephrine (but not isoproterenol) induced 2- to 3-fold increases in the rate of alpha-aminoisobutyric acid transport within 2-4 hr after a 1 hr lag. Propranolol abolished the increase in cAMP elicited by epinephrine and isoproterenol, but did not block the induction of alpha-aminoisobutyric acid transport by epinephrine. In contrast, dihydroergotamine abolished and phentolamine diminished the induction of alpha-aminoisobutyric acid transport by epinephrine but did not decrease the stimulation of cAMP levels by epinephrine. Epinephrine dose response curves for cAMP and alpha-aminoisobutyric acid transport were similar. Once exposed to epinephrine, cells became refractory to further stimulation of cAMP levels by epinephrine.

Adrenergic alpha-Antagonists↗
PubMed1976

Opposing effects of mitogenic and nonmitogenic lectins on lymphocyte activation. Evidence that wheat germ agglutinin produces a negative signal.

In an effort to clarify the mechanism by which certain plant lectins induce lymphocyte activation, we have studied amino acid (amino[14C]isobutyric acid) uptake in purified human lymphocytes exposed to mitogenic and nonmitogenic lectins. In confirmation of earlier work, mitogenic lectins (concanavalin A and two phytohemagglutinins) produced a dose-related, 2- to 10-fold increase in aminoisobutyric acid transport. Changes occurred as early as 2 hours and reached a maximum after 18 hours. The stimulation by concanavalin A was inhibited by alpha-methyl-D-mannoside but not by other selected monosaccharides, indicating that the effect is modulated through specific carbohydrate receptors. In contrast to the stimulation with concanavalin A and phytohemagglutinin, the nonmitogen wheat germ agglutinin inhibited aminoisobutyric acid transport, both in the presence and absence of the mitogenic lectins. The inhibition was seen over a broad wheat germ agglutinin dose range, was prevented by N-acetylglucosamine, a known inhibitor of wheat germ agglutinin binding, and did not appear to be associated with cytotoxicity. Comparative binding studies with radiolabeled concanavalin A and wheat germ agglutinin demonstrated that differences in transport occurred in cells containing comparable numbers of bound lectin molecules indicating that the failure of wheat germ agglutinin to stimulate a response was not a result of ineffective binding. The lack of stimulation by wheat germ agglutinin was not due to its inability to interact multivalently with membrane receptors since this lectin is divalent, produces capping and agglutination, and continues to inhibit aminoisobutyric acid transport even after the minimum valence was increased to 4 by cross-linking with glutaraldehyde. In contrast both divalent and tetravalent concanavalin A produced stimulation. Competitive binding studies with soluble wheat germ agglutinin or lectin attached to 300 A latex spheres revealed little or no competition for binding sites with radiolabeled concanavalin A, suggesting the two lectins are interacting with different receptors. This was further suggested by kinetic studies of aminoisobutyric acid transport which indicated that wheat germ agglutinin was probably affecting both the Vmax and Km of transport, whereas concanavalin A affected only the Vmax. While the mechanism by which concanavalin A and wheat germ agglutinin produce opposing effects on amino acid transport is not clear, since the two lectins appear to be interacting with different surface receptors we would suggest that they are perturbing microanatomically and functionally different domains on the lymphocyte plasma membrane.

Aminoisobutyric Acids↗
PubMed1976

Regulatory characteristics of amino acid transport in newborn rat renal cortex cells.

The uptaken of alpha-aminoisobutyric acid by slices of kidney cortex from newborn rats is enhanced by a preliminary incubation of the tissue in buffer at 37 degrees C. This effect is abolished by anaerobiosis, the presence of dinitrophenol or the removal of Na+ during the preliminary incubation. Cycloheximide (50 muM) and purimycin (1 mM) as well as alpha-aminoisobutyric acid, glycine and proline (5 mM) in the preincubation buffer also abolish the effect, while actinomycin D (0.8 muM) partially the phenomenon indicates that the enhanced uptake is due to an increased entry rate into the cells without a change in effux. There is no alteration in the apparent transport Km but an increase in the V for entry. The effect is dependent on tissue age being observed between birth and 22 days, after which there is a decrease in response to preliminary incubation with no effect seen in adult tissues.

Aging↗
PubMed1995

Chloride dependent amino acid transport in the human small intestine.

Carriers of beta amino acids and imino acids in the small intestine of rabbits and guinea pigs are chloride dependent, and a cotransport of chloride, sodium, and 2-methyl-aminoisobutyric acid has been shown. This study examines the chloride dependence of amino acid transport in the human small intestine. The steady state tissue uptake of amino acids, given as the ratio between substrate concentration in intracellular and extracellular water after 35 minutes incubation at 37 degrees C, was determined in mucosal biopsy specimens from the duodenum of patients undergoing diagnostic upper endoscopy and compared using one way analysis of variance. Uptake of leucine and alpha-methyl-D-glucoside in the duodenum and the distal ileum did not differ. The accumulation of all substrates was sodium dependent. In the absence of mucosal chloride the uptake of taurine, glycine, and 2-methyl-aminoisobutyric acid was significantly reduced while that of leucine and alpha-methyl-D-glucoside was unaffected and the reduction of beta alanine uptake not statistically significant. Uptake of 2-methyl-aminoisobutyric acid and proline showed mutual inhibition. Leucine did not reduce uptake of the beta amino acids. In conclusion, chloride dependent transport processes for 2-methyl-amino-isobutyric acid, taurine, and glycine are present in the human small intestine.

Adult↗
PubMed1982

Choline acetyltransferase in cerebral arteries: modulator of amino acid uptake?

The possibility exists that synthesis of acetylcholine in cerebral blood vessels does not reflect the presence of cholinergic nerves, but is the property of some other cell type. Therefore, the hypothesis that acetylcholine synthesis in cerebral arteries modulates amino acid transport was tested. Choline acetyltransferase activity in rabbit cerebral arteries was inhibited by (2-benzoylethyl) trimethylammonium chloride. Furthermore, the product formed in this assay was degraded by added acetylcholinesterase, confirming the authenticity of measurements of choline acetyltransferase. Rabbit pial arteries (basilar and middle cerebral) accumulated alpha-aminoisobutyric acid to a greater extent than peripheral arteries. Ouabain (10(-5) M) blocked this accumulation, suggesting that it is analogous to the A-system for amino acid transport. (2-benzoylethyl) Trimethylammonium chloride showed a concentration dependent inhibition of alpha-aminoisobutyric acid accumulation in cerebral arteries, but was without effect on peripheral arteries. Atropine and physostigmine in concentrations as high as 10(-6) M had no significant effects on alpha-aminoisobutyric acid accumulation. An association between choline acetyltransferase activity and amino acid uptake is apparent in the cerebral vasculature, suggesting that synthesis of acetylcholine may be involved in modulation of the blood-cerebrospinal fluid barrier. This finding underscores the uncertainty of assuming that acetylcholine synthesis necessarily indicates the presence of cholinergic nerves.

Acetylcholine↗
PubMed1986

Stimulation of amino acid uptake and Na+,K+-ATPase activity by norepinephrine in superior cervical sympathetic ganglia excised from adult rats.

Active uptake of a labelled nonmetabolizable amino acid, alpha-aminoisobutyric acid (AIB), into isolated superior cervical sympathetic ganglia (SCG) excised from adult rats was considerably stimulated by the addition of either norepinephrine (NE, 50 microM) or 3,4-dihydroxyphenylethylamine (dopamine, DA, 100 microM) to the medium during aerobic incubation for 2 h at 37 degrees C. The NE-induced increase in AIB uptake was significantly antagonized by the addition of an alpha 1-adrenoceptor antagonist (prazosin, 10 microM) in SCG axotomized 1 week prior to the examination, in which most of the ganglionic neurons had degenerated and reactive proliferation of the satellite glial components was in progress. The addition of neither acetylcholine (ACh, 1 mM) plus eserine (0.1 mM) nor cyclic nucleotides (1 mM) changed the AIB uptake by the SCG. In the axotomized SCG, the NE-evoked increase in AIB uptake was much more pronounced than that of intact or denervated SCG. A kinetic study of the active AIB uptake in the SCG showed that NE produced a decrease of the Km value and an increase in the Vmax, especially in the axotomized SCG. Ganglionic Na+, K+-ATPase activity was greatly stimulated in the presence of NE, but not by ACh. These results strongly suggest that the NE-induced enhancement of active AIB uptake in the isolated SCG is occurring in glial cells rather than in neuronal cells, with a possible alteration of membrane properties for amino acid uptake and with an apparent regulation by the stimulated transport enzyme Na+, K+-ATPase.

Acetylcholine↗
PubMed1982

Increase in K+ and alpha-AIB active transport in CHO cells after low [K+] treatment.

We have studied the effects of prolonged incubation in low [K+] medium (approximately 0.3 mM) on both K+ and amino acid transport in Chinese hamster ovary (CHO) cells. When incubated in low [K+] medium, CHO cells redressed partially the loss of intracellular K+ after 12 h. After 24 h of incubation, both the activity of Na+-K+-ATPase in crude homogenates, and the transport capacity (Vmax) for ouabain-sensitive (i.e., active) K+ influx approximately doubled. The magnitude of the ouabain-insensitive (i.e., passive) K+ influx decreased by 50%. Thus the regulatory response involves an apparent increase in Na+-K+ pump and a decrease in K+ leak. The transport capacity for the nonmetabolized amino acid, alpha-aminoisobutyric acid (alpha-AIB), also increased after 24 h in low [K+] medium. The Vmax for the Na+-dependent (i.e., active) alpha-AIB influx increased by about 150%, and the magnitude of the Na+-independent influx increased by 20-40%. These changes in alpha-AIB transport result in a twofold greater capacity to accumulate this amino acid. Thus the regulation of K+ and alpha-AIB transport systems appears to be linked and possible mechanisms of this linkage are discussed.

Aminoisobutyric Acids↗
PubMed1991

New substrates of the multispecific bile acid transporter in liver cells: interference of some linear renin inhibiting peptides with transport protein(s) for bile acids.

Interactions between some stable linear peptides with renin inhibitory activity and a multispecific transport system in the basolateral plasma membrane of liver cells was studied on cell suspensions. The peptides used in our experiments were taken up by liver cells and subsequently eliminated without any biotransformation (e.g., proteolysis). No degradation products could be detected in the extracellular medium by thin-layer chromatography. All peptides tested inhibited the uptake of physiological and of some foreign substrates of the multispecific bile acid transporter (MT). The phalloidin response of liver cells was also inhibited to a similar degree in a concentration-dependent manner. The potency of inhibition did not correlate with the lipophilic properties of the peptides. On the other hand a tight correlation could be documented between the inhibition of cholate transport and that of the phalloidin response. Transport inhibition of typical substrates of the MT by the above renin inhibitors was competitive. In contrast, the transport of a typical substrate of the bilirubin carrier (rifampicin), of amino acids (alpha-aminoisobutyric acid), long chain fatty acids (oleic acid) and cationic compounds (thiamin hydrochloride) was not inhibited by the same renin inhibitors. These results indicate that linear renin inhibiting peptides are taken up into liver cells by carrier proteins related to the MT.

Aminoisobutyric Acids↗
PubMed1985

Rapid amino acid uptake in rat pituitary neural lobe during functional stimulation by chronic dehydration.

We studied the transfer of a small neutral amino acid, alpha-aminoisobutyric acid, from arterial blood into the pituitary neural lobe in normal rats and in rats deprived of water for 5 days. A threefold increase in the neural lobe uptake of the amino acid was found in the chronically dehydrated rats. Possible causes for this effect include enlargement of the capillary and pituicyte membrane surface areas available for solute flux and increased permeability of these membranes. Such functional and structural alterations may be associated with an increase in protein turnover in the neural lobe during dehydration.

Aminoisobutyric Acids↗
PubMed1988

In vitro toxicity assessment of cyclosporin A and its analogs in a primary rat hepatocyte culture model.

The cytotoxicity of cyclosporin A (CsA), a widely used immunosuppressant drug, was evaluated in primary cultures of rat hepatocytes. Furthermore, the concentration-dependent (10(-7) to 10(-5) M) cytotoxic effects of the cyclosporin analogs, CsG, CsH, CsF, and of a major metabolite of CsA, CsA/M17, were assessed in an attempt to classify the different cyclosporin analogs according to their in vitro hepatotoxic potential. All compounds invariably inhibited the net release of taurocholate (de novo synthesized from cholate added to the extracellular medium). This sensitive functional marker did not discriminate between the structural analogs. In addition, all compounds inhibited, to various extents, the biosynthesis and secretion of proteins without affecting the uptake rate of the nonmetabolizable amino acid, alpha-aminoisobutyric acid. These functional changes occurred in the absence of overt irreversible cell damage (no leakage of lactic dehydrogenase up to 10(-5) M cyclosporin during 17 hr of incubation). The relative toxic potential of the drug congeners (CsG greater than CsA greater than CsH = CsF = CsA/M17) correlated well with the degree of their accumulation in the hepatocytes during exposure to equimolar drug concentrations.

Aminoisobutyric Acids↗
PubMedDate not supplied

Proteolytically stable peptides by incorporation of alpha-Tfm amino acids.

A series of model peptides containing alpha-trifluoromethyl-substituted amino acids in five different positions relative to the predominant cleavage site of the serine protease alpha-chymotrypsin was synthesized by solution methods to investigate the influence of alpha-Tfm substitution on the proteolytic stability of peptides. Proteolysis studies demonstrated absolute stability of peptides substituted to the P1 position and still considerable proteolytic stability for peptides substituted at the P2 and P'2 positions compared with the corresponding unsubstituted model peptide. Comparison with peptides containing the fluorine-free disubstituted amino acid alpha-aminoisobutyric acid allowed to separate electronic from steric effects. Furthermore, the absolute configuration of the alpha-Tfm-substituted amino acid was found to exert considerable effects on the proteolytic stability, especially in P'1 substituted peptides. Investigations of this phenomenon using empirical force field calculations revealed that in the (S,R,S)-diasteromer the steric constraints exhibited by the alpha-Tfm group can be outweighed by an advantageous interaction of the flourine atoms with the serine side chain of the enzyme. In contrast, a favourable interaction between substrate and enzyme is impossible for the (S,S,S)-diastereomer.

Aminoisobutyric Acids↗
PubMed1996

Interactions between angiotensin II and adenosine 3':5'-cyclic monophosphate in the regulation of amino acid transport by vascular smooth muscle cells.

The regulation of amino acid transport by angiotensin II (AII) and cyclic AMP (cAMP) was assessed in cultured vascular smooth muscle cells, using a nonmetabolizable amino acid, alpha-[3H]aminoisobutyric acid (AIB). An exposure time in excess of 2 h was required for AII to elicit a stimulatory response, the magnitude of which increased in a time-dependent manner for 12 h. AII-induced transport was blocked by [1-sarcosine, 8-isoleucine]AII, a competitive inhibitor of AII binding. The effect of AII was not abolished by downregulation protein kinase C with phorbol 12,13-dibutyrate or by use of a protein kinase C inhibitor, suggesting that transport in response to AII can be mediated by a protein kinase C independent pathway. In contrast, the elimination of calcium from the incubation medium reduced AII-stimulated AIB uptake. The calmodulin inhibitor N-(6-aminohexyl)-5-chloro-1-naphthalenesulfonamide partially inhibited AIB uptake in response to AII, suggesting that calmodulin may be involved in the modulation of AII-stimulated amino acid transport. AIB transport was also increased by elevating intracellular cAMP levels via beta-adrenergic receptor stimulation, the use of a cAMP analog (N6-monobutyryl cAMP), or a phosphodiesterase inhibitor (3-isobutyl-1-methylxanthine) or by direct stimulation of adenylate cyclase with forskolin. cAMP-induced AIB transport was evident within 10 min and peaked within 1 h. At 1 h AII enhanced cAMP-stimulated AIB transport. A possible mechanism for this effect is suggested by the observation that AII potentiated cAMP production in response to isoproterenol and 3-isobutyl-1-methylxanthine.

1-Methyl-3-isobutylxanthine↗
PubMed1987

The microcirculation of rat circumventricular organs and pituitary gland.

Blood volume, blood flow, and blood-to-tissue transfer of an amino acid in circumventricular organs, such as the median eminence and subfornical organ, and the pituitary gland of conscious rats were measured by using quantitative autoradiographic techniques and computer-assisted processing of the tissue images. Retained erythrocyte and plasma volumes observed in circumventricular organs and the anterior and neural lobes of the pituitary gland were dissimilar but in all cases greater by several times than those in cerebral grey matter; these findings suggest the presence of a dense network of high-resistance microvessels in circumventricular organs. The rate of capillary blood flow in the subfornical organ and median eminence was similar to that of grey matter, whereas blood flow in the pituitary neural lobe was several times higher than in grey matter. Thus the apparent velocity of intracapillary blood flow is much higher in the neural lobe than in the subfornical organ. Blood-to-tissue transfer of a small neutral amino acid, alpha-aminoisobutyric acid, was 200 to 700 times more rapid in circumventricular organs and pituitary neural lobe than in the inferior colliculus and caudate nucleus, structures having a blood-brain barrier (BBB). Morphometric analyses indicated that capillary volume and surface area were two times larger in the neural lobe than in the subfornical organ. Moreover, capillaries of the neural lobe and subfornical organ had numerous endothelial fenestrations and cytoplasmic pits or vesicles, whereas capillaries of the inferior colliculus had no fenestrations and fewer vesicles. These studies demonstrate quantitative differences in the microcirculatory systems not only between circumventricular organs and BBB structures but also among circumventricular organs.

Aminoisobutyric Acids↗
PubMed1983

Regulation of membrane transport sites for amino acids in myogenic cells. A differentiation dependent phenomenon.

Myoblasts from 12-day chick embryos in cell culture transport the nonmetabolizable amino acid alpha-aminoisobutyric acid (AIB) two to three-fold more rapidly than multinucleated myotubes which form from them. This decrease in transport is due to a relative decrease in the number of transport sites per unit area of cell surface suggesting a compositional change in the plasma membrane during myogenesis. In studies reported here, AIB transport was monitored throughout myogenesis and correlated with other aspects of differentiation. During myogenesis the number of amino acid transport sites remains constant per myotube nucleus. As myogenesis proceeds, there is a marked increase in cellular protein and cell surface without a commensurate increase in amino acid transport sites. The net consequence of the surface area change is fewer amino acid transport sites per unit area of myotube membrane surface. The decrease in membrane transport sites for AIB per unit area of membrane is not a result of length of time in culture per se, medium depletion, or cell density, but is a result of differentiation, since blocking myoblast fusion by deprivation of calcium delays the decrease in AIB transport sites per unit cell surface area while reversal of the calcium deprivation block is accompanied by a rapid decrease in the number of AIB transport sites per unit cell surface area. Thus, the decrease in AIB transport sites is an aspect of differentiation which accompanies the marked elaboration of surface membrane during myogenesis.

Aminoisobutyric Acids↗
PubMed1996

Ontogeny of blood-brain barrier function in ovine fetuses, lambs, and adults.

The ontogeny of regional blood-brain barrier function was quantified with the rate constant for influx (Ki) across the blood-brain barrier with the small molecular weight synthetic, inert hydrophilic amino acid alpha-aminoisobutyric acid (AIB) in chronically instrumented early (87 days of gestation, 60% of gestation) and late (137 days of gestation, 90% of gestation) gestation fetal, newborn (3 days of age), older (24 days of age), and adult (3 years of age) sheep. The Ki was significantly (P < 0.05) lower in the brain regions of the adult sheep and in most brain regions of newborn and older lambs compared with fetuses at 60 and 90% of gestation. The Ki exhibited regional brain heterogeneity (P < 0.05) in the five groups. The patterns of regional heterogeneity were accentuated (P < 0.05) in the younger groups. We conclude that ontogenic decreases in blood-brain barrier permeability are observed in ovine fetuses from 60% of gestation to maturity in the adult.

Aging↗
PubMed1984

Induction of amino acid transport by L-triiodothyronine in cultured growth hormone-producing rat pituitary tumor cells (GC cells).

The action of L-triiodothyronine (T3) on amino acid transport in the GC clonal strain of rat pituitary cells was investigated by measurement of the uptake of the nonmetabolizable amino acid, alpha-aminoisobutyric acid (AIB). The uptake of AIB by GC cells appeared to require energy and Na+ and displayed Michaelis-Menten kinetics. In comparison to cultures maintained in the absence of T3, T3 addition resulted in an increase in AIB uptake which seemed due to an increase in the initial rate of AIB transport. T3 addition resulted in increased AIB accumulation at later time points as well. T3 induction of AIB transport did not occur until 3.5 h after addition of T3, and this effect was blocked by cycloheximide. Maximal induction occurred 48 to 72 h later. One-half maximal induction occurred 24 to 48 h after addition of T3. No detectable changes either in AIB uptake or intracellular water space, measured by uptake of the nonmetabolizable sugar, 3-O-methyl-D-glucose, were noted for the first 120 min after addition of T3. Induction of AIB transport occurred at 0.05 nM T3 (total medium concentration) and one-half maximal induction occurred at 0.17 nM T3. The relative potencies of four iodothyronine analogues for AIB transport were in accord with their reported activities in nuclear T3 receptor binding assays. These data suggest that induction of AIB transport by T3 may be mediated by the nuclear T3 receptor and may reflect the pleiotrophic response of GC cells to thyroid hormone.

3-O-Methylglucose↗
PubMed1976

Amino acid transport in follicles isolated from the rabbit ovary.

The model amino acid alpha-aminoisobutyric acid (AIB) has been used to investigate amino acid transport in follicles isolated from rabbit ovaries. LH markedly increased AIB transport, while incubation with FSH, cAMP or dbcAMP failed to increase the process. Several kinds of inhibitors have been utilized to characterize follicular AIB transport as an energy dependent process and apparently independent of follicular steroidogenesis. The rates of AIB efflux from preloaded follicles were measured in the presence and absence of LH; the rate measurements suggest that only the rate of entry of AIB into follicular cells is stimulated by the gonadotropin. Further experiments used inhibitors of RNA and protein synthesis to examine the relationship between AIB transport and the synthesis of macromolecules. Whereas blocking RNA synthesis suppressed the LH effect on AIB transport, inhibitors of protein synthesis increased the rate of AIB movement into follicles. The in vitro transport of AIB was also studied in follicles isolated 2 hr after mating and in ovulated follicles which were obtained 12 h after coitus. AIB transport rate showed a rise following mating but fell to less than precoital rates in ovulated (12 h) follicles. Transport in both 2 and 12 h follicles proved unresponsive to LH stimulation. Taken together, these studies suggest that AIB transport in isolated ovarian follicles is a LH-sensitive, energy-dependent process. Although AIB transport changes in a pattern qualitatively similar to that previously reported for postcoital protein synthesis, LH stimulation of the two processes may be via different mechanisms.

Aminoisobutyric Acids↗