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PubMed1986

Acetaldehyde inhibition of protein synthesis in isolated rat pancreatic acini.

Exposure of isolated dispersed pancreatic acini to increasing concentrations of ethanol (5 to 500 mM) or acetaldehyde (0.5 to 100 mM) produced a progressive inhibition of [3H]leucine incorporation into both "cellular" (those remaining in the cell) and "secretory" (those released into the medium) proteins. Whereas 500 mM ethanol caused 90-95% inhibition in the synthesis of "cellular" and "secretory" proteins, the concentration of acetaldehyde needed to produce a similar inhibition was found to be 50 mM. All subsequent experiments were performed with 12.5 mM acetaldehyde, a concentration that consistently inhibited acinar protein synthesis by about 50%. The acetaldehyde-mediated inhibition of acinar protein synthesis was partially normalized when this metabolite was removed after 30 min during a 90-min incubation period. In the presence of acetaldehyde, the secretion of 3H-pulse-labeled proteins, but not amylase, trypsinogen, or chymotrypsinogen, was greatly depressed. Acetaldehyde also caused a marked reduction in [3H]uridine incorporation into acinar RNA. The entry of [3H]uridine, [3H]leucine, and [3H]aminoisobutyric acid into isolated acini was found to be slightly (15-25%) decreased by acetaldehyde. It is concluded that acetaldehyde exerts a direct toxic effect on isolated dispersed pancreatic acini as evidenced by diminution of both protein and RNA synthesis and decreased secretion of the newly synthesized proteins. This inhibitory effect of acetaldehyde could be partially reversed.

Acetaldehyde↗
PubMed1988

High intensity light exposure increases blood-brain barrier transport in rats.

A quantitative technique utilizing 14C-alpha-aminoisobutyric acid as a tracer was used to study the blood-brain barrier permeability modifications induced by environmental stimuli, as the high intensity light exposure. The blood-to-brain transfer constant was significantly increased only in the occipital cortex following the treatment. The possibility that the blood-brain barrier is able to modify its local characteristics in response to cerebral activity changes was discussed.

Aminoisobutyric Acids↗
PubMed1990

The longest, regular polypeptide 3(10) helix at atomic resolution.

A synthetic, terminally blocked homodecapeptide from the C alpha, alpha-dimethylated glycyl residue alpha-aminoisobutyric acid has been analyzed by single-crystal X-ray diffraction and the structure refined to R = 0.073. The compound crystallizes as a perfect 3(10) helix, stabilized by eight consecutive intramolecular N-H . . . O = C hydrogen bonds. This is the first observation at atomic resolution of a regular polypeptide 3(10) helix as long as three complete turns.

Aminoisobutyric Acids↗
PubMed1969

Interaction of estrogen and progesterone in chick oviduct development. I. Antagonistic effect of progesterone on estrogen-induced proliferation and differentiation of tubular gland cells.

Daily administration of estrogen to immature female chicks results in marked oviduct growth and appearance of characteristic tubular gland cells which contain lysozyme. Although a rapid increase in total DNA and RNA content begins within 24 hr, cell specific protein, lysozyme, is first detectable after 3 days of estrogen. Progesterone administered concomitantly with estrogen antagonizes the estrogen-induced tissue growth as well as appearance of tubular gland cells and their specific products, lysozyme and ovalbumin. When the initiation of progesterone administration is delayed for progressively longer periods (days) during estrogen treatment, proportionally greater growth occurs with more lysozyme and tubular gland cells after 5 days of total treatment. Progesterone does not inhibit the estrogen-stimulated increase in uptake of alpha-aminoisobutyric acid and water by oviduct occurring within 24 hr or the estrogen-induced increase in total lipid, phospholipid, and phosphoprotein content of serum. The above results of progesterone antagonism can best be explained by the hypothesis that progesterone inhibits the initial proliferation of cells which become tubular gland cells but does not antagonize the subsequent cytodifferentiation leading to the synthesis of lysozyme and ovalbumin once such cell proliferation has occurred.

Aminoisobutyric Acids↗
PubMed1988

Characterization of functional type I insulin-like growth factor receptors from human choriocarcinoma cells.

Specific receptors for insulin-like growth factor I (IGF-I) on cultured human choriocarcinoma cells (JEG-3 and BeWo) were characterized. The binding of 125I-labeled recombinant (Thr59)IGF-I to the cells was reversible and time, temperature, and pH dependent. Steady state of binding occurred after 16 h at 4 C, pH 7.4. Natural human IGF-I (hIGF-I), hIGF-II, recombinant (N-Met)IGF-I, rat multiplication-stimulating activity, and insulin were 200%, 37%, 37%, 1.6%, and 0.1% as potent as (Thr59)IGF-I in inhibiting the binding of [125I]iodo-(Thr59)IGF-I to JEG-3 cells, respectively. Epidermal growth factor was ineffective. The half-maximal displacement of [125I]iodo-(Thr59)IGF-I by unlabeled (Thr59)IGF-I occurred at 11 +/- 2 ng/ml (mean +/- SEM) in both JEG-3 and BeWo cells. Scatchard analysis of the competitive binding data revealed linear plots indicating a single species of binding sites with an association constant of 0.8 X 10(9) M-1 for the binding of [125I]iodo-(Thr59)IGF-I to both cell lines. The binding capacity was 30,000 and 20,000 sites/cell for JEG-3 and BeWo cells, respectively. Chemical cross-linking of [125I]iodo-(Thr59)IGF-I to JEG-3 cells revealed two receptor complexes of 130K and 260K. Their formation was completely inhibited by an excess of unlabeled (Thr59)IGF-I or hIGF-II. Increasing amounts of insulin affected both labeled bands equally, suggesting that the 130K and 260K bands represent the monomer and dimer forms, respectively, of the ligand-binding alpha-subunit of type I IGF receptor. (Thr59)IGF-I, in a dose-dependent manner, stimulated uptake of nonmetabolizable alpha-[3H]aminoisobutyric acid by JEG-3 cells, showing that the receptor is biologically active. Our results demonstrate that choriocarcinoma cells possess functional high affinity type I IGF receptors and suggest that IGF-I is involved in the growth-regulating processes of JEG-3 and BeWo cells. These cells may provide a useful model to study the role of IGFs in trophoblast physiology.

Aminoisobutyric Acids↗
PubMed1977

The regulation by fibroblast growth factor of early transport changes in quiescent 3T3 cells.

This study involves the use of fibroblast growth factor (FGF) as a substitute for exogenous serum to examine the early transport changes which occur when quiescent 3T3 cells re-initiate active growth. FGF, in nanogram amounts, together with insulin and dexamethasone, can induce mitogenesis and mitosis in 3T3 cells GO-arrested by holding in growth medium containing 0.8% calf serum. In terms of quiescent cell transport activity enhancement, FGF is 300,000-fold more effective than fresh serum, on a protein basis. In addition, very short exposure of serum-depleted cells to FGF indicates that a distinct temporal or time sequence exists in the transport system activation process. For example, uptake of alpha-aminoisobutyric acid (AIB) and uridine are stimulated very rapidly, whereas hypoxanthine uptake does not respond until much later. Closer analysis shows that AIB uptake is maximally enhanced within zero to two minutes after FGF addition to cells. Finally, the stimulatory effect of FGF on transport system activities is specific in terms of the proliferative state of the cells to which it is added, and in terms of the uptake systems which respond to it.

Adenosine↗
PubMed1979

Sex difference in the accumulation of D-beta-aminoisobutyrate in organs of mouse after thymine loading.

The concentration of D-beta-aminoisobutyric acid (D-BAIB) in the liver and kidney was twice as high and dropped more slowly in the female mouse than in the male after an intraperitoneal injection of thymine. The concentration of beta-alanine, formed from uracil by the same enzyme system catalyzing formation of D-BAIB from thymine, was not different in the liver and kidney of both sexes after an intraperitoneal injection of uracil. After the intraperitoneal injection of D-BAIB, the concentration of BAIB in male liver decreased faster than that in female liver. Inhibition of D-BAIB: pyruvate aminotransferase caused by injection of D-cycloserine resulted in a significant increase in the concentration of BAIB in liver of both sexes after injection of thymine, but the concentration dropped more rapidly in the male. The activity of D-BAIB: pyruvate aminotransferase was not different in the livers of male and female mice. Under the action of probenecid, an inhibitor of active transport systems, the sex difference in accumulation and disappearance of the amino acid in the liver was not observed. This suggested that the excretion of BAIB is more active in the renal tubules of the male mouse than in those of the female. However, the amount of BAIB excreted in the urine after injection of thymine was larger in the female mice than in the male mice. There may be another probenecid-sensitive enzyme for the disposal of BAIB in male mice.

Aminoisobutyric Acids↗
PubMed1974

A soluble super-active form of insulin.

Insulin-like material can be extracted from insulin-Sepharose. This soluble material elicits super-insulin responses from mammary epithelial cells. It stimulates the accumulation of alpha-aminoisobutyric acid by virgin mouse mammary cells, which are unresponsive to insulin itself. It exerts a greater stimulatory effect on mammary cells from pregnant mice than insulin. It also is more efficacious than insulin as a stimulant of DNA synthesis and the combined activities of glucose-6-phosphate dehydrogenase (EC 1.1.1.49) and phosphogluconate dehydrogenase (EC 1.1.1.43). Its specific biological activity on these cells is more than five times greater than that of insulin.

Aminoisobutyric Acids↗
PubMed1978

Uridine diphosphate N-acetylglucosamine stimulates uptake of nutrients by quiescent BALB/C3T3 cells.

Preincubation of quiescent BALB/C3T3 cells with uridine diphosphate N-acetylglucosamine (UDP-GlcNAc) in conditioned medium resulted in a time- and concentration-dependent stimulation of uptake of 2-deoxyglucose, uridine, and alpha-aminoisobutyric acid over that seen in conditioned medium alone. The apparent Km values for 2-deoxyglucose and uridine uptake were the same for cells incubated with or without UDP-GlcNAc, whereas the Vmax values were higher for cells pretreated with the nucleotide sugar. The stimulation of uptake was specific for UDP-GlcNAc, and the other nucleotide sugars tested were ineffective; incubation of UDP-GlcNAc-pretreated cells with N-acetylglucosaminidase abolished the stimulatory effect. In all cases, the extent of stimulation of nutrient uptake was comparable to that seen with serum-stimulated cells. Incubation of quiescent cells in situ with UDP-[3H]GlcNAc led to incorporation of radioactive N-acetylglucosamine into the acid-precipitable fraction; a large fraction of the labeled amino sugar was found on the cell surface acceptors. We interpret these data to mean that the cellular acceptors of quiescent cells are "under-glycosylated," at least in terms of N-acetylglucosamine, and that stimulation of uptake of nutrients may be a consequence of restoration of the amino sugar residues on the oligosaccharide chains of acceptors on the cell surface.

Acetylglucosamine↗
PubMed1975

Stimulation of protein synthesis in cultured heart muscle cells by glucose.

Glucose stimulated the rate of incorporation of [3H]leucine into HCLO4-insoluble fraction of cultured rat heart muscle cells under both aerobic and anaerobic conditions. In the aerobic system the incorporation proceeded at a constant rate during 3h of incubation with and without glucose whereas in the anaeorbic system the incorporation ceased after approx. 60 min and could be renewed only by the addition of glucose. No correlation was found to exist between the above effect of glucose on protein synthesis and glucose-dependent changes in the intracellular ATP concentration. The extent of the stimulation of protein synthesis was related to the concentration of glucose. The effect of glucose was suppressed by cycloheximide but was not affected by actinomycin D. Glucose had no effect on the rate of transport of alpha-aminoisobutyric acid. Mannose also stimulated [3H]leucine incorporation. Substances that did not produce lactate were ineffective. Iodoacetate inhibited the stimulatory effect of glucose, but pyruvate, which by itself had no apprecialbe stimulatory action, relieved the inhibition induced by iodoacetate. There was no concomitant change in the concentration of ATP when iodoacetate inhibition was reversed by pyruvate. L-Lactate or other intermediates of energy metabolism could not relieve the inhibitory effect of iodoacetate.

Adenosine Triphosphate↗
PubMed1988

Effect of T3 on insulin action, insulin binding, and insulin receptor kinase activity in primary cultures of rat hepatocytes.

In vivo studies have demonstrated that the liver is the main site of insulin resistance in hyperthyroidism. To further investigate the effect of thyroid hormone in the liver, we have incubated primary cultures of rat hepatocytes in the presence and absence of triiodothyronine (T3) 1 ng/ml and 5 ng/ml for 20 hr. Without affecting basal activity, T3 5 ng/ml decreased insulin-stimulated (1 x 10(-7) M) lipid synthesis but not insulin-stimulated alpha-aminoisobutyric acid uptake. These changes occur in the absence of any abnormalities in 125I-insulin binding, degradation, internalization or insulin receptors structure as determined by affinity-labeling methods. However, basal insulin receptor kinase activity using Glu4: Tyrl as phospho-acceptor was decreased by T3 without altering its insulin responsiveness. These results demonstrate the heterogeneity of T3's effects at the postinsulin binding level in the liver.

Aminoisobutyric Acids↗
PubMed1980

Taurine release from the pineal-gland is stimulated via a beta-adrenergic mechanism.

Pineal glands were prelabeled in organ culture with [14C]taurine, and then treated with biogenic amines. The rate of release of [14C]taurine was rapidly elevated by low concentrations of norepinephrine, apparently acting through a beta-adrenergic mechanism. The release was probably not due to a nonspecific change in membrane permeability, as a comparable release was not seen with [14C]glycine and [14C]alpha-aminoisobutyric acid. These findings suggest that the release of taurine may be related to or a reflection of the early events in adrenergic activation of the pineal gland, such as hyperpolarization of pinealocytes. The released taurine might also have an extracellular role as it has been recently shown that extracellular taurine can interact with pineal beta-adrenergic receptors to stimulate melatonin production. Thus, the released taurine could possibly act as an extracellular feedback messenger.

Acetyltransferases↗
PubMed1984

Alpha 1-adrenergic inhibition of protein synthesis in rat submandibular cells.

The incorporation of [14C]leucine into protein in dispersed cells from rat submandibular gland was inhibited by epinephrine. The dose required for a half-maximal effect was approximately 10(-6) M. This sensitivity is similar to that of mucin and potassium secretion induced by epinephrine from these cells. The inhibitory effect of epinephrine was mediated by the activation of alpha 1-adrenergic receptors and was partially independent of extracellular calcium. The calcium ionophore A23187 also decreased protein synthesis in the presence and absence of extracellular calcium. Epinephrine diminished alpha-[14C]aminoisobutyric acid (AIB) influx, but the extent of altered AIB uptake was much less than the extent of decrease in protein synthesis. Analysis of newly synthesized protein by gel electrophoresis and autofluorography showed that epinephrine selectively inhibited the synthesis of specific submandibular proteins. In aggregate these results suggest that activation of alpha 1-adrenergic receptors in rat submandibular cells influences the regulation of protein synthesis by a mechanism that uses intracellular calcium.

Adrenergic alpha-Agonists↗
PubMed1997

Helical preferences of alanine, glycine, and aminoisobutyric homopeptides.

The stability between helical conformations of homopeptides of alanine, glycine, and aminoisobutyric acid has been studied by means of quantum-mechanical methods. The influence of peptide length on the relative stability between helical conformations has also been analyzed by means of systematic studies for peptides of size up to 11 residues. Finally, the influence of the solvent has been examined by using self-consistent reaction field methods. The results provide a detailed picture of the modulation exerted by these factors on the helical preferences of these peptides.

Alanine↗