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At least 1,297 records · Page 72Linked to original sources
PubMed1985

Specificity of intestinal brush-border proline transport: cyanine dye studies.

The ability of rabbit jejunal brush borders to transport inhibitors of the imino carrier was investigated in membrane vesicles by measuring their ability to depolarize the membrane potential. Membrane potentials were monitored using a voltage-sensitive cyanine dye. Piperidine and pyrrolidine carboxylic acids, which are potent inhibitors of Na+-dependent proline transport (Ki less than 0.5 mM) depolarize the potential in a Na+-dependent, saturable manner indicating transport. On the other hand, N-methylated amino acids, which are fair inhibitors (Ki 2-10 mM), do not depolarize the membrane to any significant extent, but they competitively inhibit the L-proline transport signal. This indicates that these analogs are nontransported inhibitors of the imino carrier. The poor inhibitors niacin and pipolinic acid (Ki greater than 60 mM) depolarize the membrane about twice as much as proline and with low Kf values. This suggests separate carriers for these substrates.

Amino Acids↗
PubMed1987

L-proline uptake in human fibroblasts: evidence for a high-affinity system in addition to system A.

Proline uptake was studied in human skin fibroblasts by simultaneous running of kinetic and inhibition experiments on the same cell lines. Two systems for proline uptake were shown: a high-affinity system not inhibited by alpha-(methylamino)isobutyric acid and a low affinity system inhibited by this amino acid (i.e. system A). These results appear to be of interest, firstly because up till now, system A was considered preferable for proline uptake in human fibroblasts, and secondly because they illustrate the need for combined inhibition and kinetic studies of amino acid uptake, especially when the substrate concentration range used and the respective Km of the systems do not allow their detection by kinetic analysis alone. Furthermore, this high-affinity system may have major physiological implications.

Aminoisobutyric Acids↗
PubMed1989

Macrophage-mediated N-nitrosation of thioproline and proline.

Thioproline (Thiazolidine-4-carboxylic acid) and proline were nitrosated by stimulated mouse macrophages in vitro. A macrophage cell line (J774.1, 1.0 x 10(6)/well, 1 ml) was incubated with Escherichia coli lipopolysaccharide, interferon-gamma and thioproline (5 mM) or proline (5 mM). After 72 hr incubation at 37 degrees C, 4 microM N-nitrosothioproline was produced. The amount of N-nitrosoproline was much lower than that of N-nitrosothioproline. Thioproline and proline inhibited the formation of carcinogenic N-nitrosomorpholine. N-nitrosothioproline and N-nitrosoproline are found as major N-nitroso compounds in human urine. Macrophage mediated N-nitrosation may contribute to the formation of these N-nitrosamino acids in the human body.

Animals↗
PubMed1991

Conserved positioning of proline residues in membrane-spanning helices of ion-channel proteins.

Proline residues are a common feature of known and putative transmembrane helices of transport proteins. We find considerable consistency in the positioning of these residues within the structures. The proline residues are usually found on the hydrophilic (interior) faces of the pore-forming helices. This general observation adds considerable support to hypotheses concerning the structure of the ion-channels formed by alamethicin and melittin. As proline kinks helices, our observation suggests that the pores formed in ion-channel proteins tend to be funnel-shaped having a constriction near their center. Such a structure can aid in the capture of ions by the channel (an entropic effect) and should help in the gating mechanism of the channel. The observation will aid identification of putative transmembrane helices of ion-channels.

Animals↗
PubMed1985

Uptake of proline by brushborder vesicles isolated from human kidney cortex.

Proline transport into renal brushborder membrane vesicles isolated from human kidney is mediated by two uptake systems. The high-affinity system is stimulated by a Na gradient and appears to be shared with glycine while the low-affinity system is not. Uptake curves of low concentrations of proline exhibit a Na-gradient-dependent overshoot indicative of electrogenic transport. The proline transport systems observed in isolated human renal brushborder membrane vesicles appear to have characteristics similar to those in rat kidney membranes.

Alanine↗
PubMed1987

Elimination of isoproterenol-induced proline-rich protein biosynthesis in rat salivary glands after adult thyroidectomy.

Surgical thyroidectomy of adult rats resulted in a gradual decrease in beta-adrenergic receptor density on the cell surface of parotid and submandibular glands. The decrease in beta-adrenergic receptors was 29 and 50% by 2 and 4 weeks, respectively, for the parotid gland. In the submandibular gland, a decrease of 50% of the total beta-receptor density was evident after 2 weeks. After 4 weeks no further decrease in beta-adrenergic receptor was observed. Subsequent challenge of the salivary glands with chronic treatment of isoproterenol (beta-adrenergic receptor agonist) failed to induce proline-rich protein and glycoprotein biosynthesis in the submandibular gland 2 weeks after thyroidectomy, whereas the parotid gland showed induced proline-rich protein but not the glycoprotein synthesis. By 4 weeks the parotid gland did not show the induced synthesis of the glycoprotein or proline-rich proteins. The inability to induce protein synthesis was reflected by decreased cAMP accumulation in both glands after injection with isoproterenol. Partial reversal of these effects on protein synthesis and cAMP accumulation was obtained by triiodothyronine treatment of thyroidectomized rats.

Animals↗
PubMed1975

Evaluation of [3-H]proline for radioautographic tracing of axonal projections in the teleost visual system.

The efficacy of [3-H]proline radioautography for tracing retinal ganglion cell projections to the optic tectum of the jewel fish, Hemichromis bimaculatus, has been compared with that of degeneration techniques. There was good agreement between the various methods. Retinal projections to the optic tectum of two other teleosts, the oscar, Astronotus ocellatus, and the goldfish, Carrasius auratus, were examined radioautographically. In addition to conventional methods of analysis, radioautograms were scanned in a slit microdensitometer and by an automated isodensity scanning system. Results of studies with the protein synthesis inhibitor, cycloheximide, are compatible with the suggestion that axonally transported proteins labeled with [3-H]proline may release diffusible precursors that are reincorporated into protein in adjacent regions. The possible advantages and limitations of radioautography of [3-H]proline-labeled axonally transported protein in brief or extended studies are discussed in terms of the results obtained in the teleost visual system.

Animals↗
PubMed1980

Radioautographic evidence for both orthograde and retrograde axonal transport of labeled compounds after intraocular injection of [3H]proline in the lamprey (Lampetra fluviatilis).

[3H] Proline injected intraocularly in lampreys has been shown to be bidirectionally transported: 24--96 h after the injection, retinofugal fibers and terminals as well as nerve cell bodies at the origin of the retinopetal system were intensely labeled. These results are at variance with the generally held belief that [3H]proline is taken up only by cell bodies and transported by the anterograde flow. The significance of the retrograde axonal transport of [3H]proline in the lamprey retinopetal system is discussed.

Animals↗
PubMed1994

Synthesis of a glycopeptide with phytoalexin elicitor activity. I. Synthesis of a triglycosyl L-serine and a triglycosyl L-seryl-L-proline dipeptide.

A stereocontrolled synthesis of the model compound for the phytoalexin elicitor-active glycoprotein is described. Glycosylation of the disaccharide, 2,3,4,6-tetra-O-acetyl-beta-D-glucopyranosyl-(1-->6)-2,3,4-tri-O-acetyl- alpha- D-mannopyranosyl trichloroacetimidate, with N-(carbobenzoxy)-(2,3,4-tri-O-acetyl-alpha-D-mannopyranosyl)-(1-->3)-L- serine methyl ester or N-(carbobenzoxy)-(2,3,4-tri-O-acetyl-alpha-D-mannopyranosyl)-(1-->3)-L- seryl-L- proline methyl ester by use of AgOTf gave the desired trisaccharide-serine or trisaccharide-seryl-proline derivatives, which were transformed into beta-D-glucopyranosyl-(1-->6)-alpha-D-mannopyranosyl-(1-->6)-alpha-D- mannopyranosyl-(1-->3)-L-serine and triglycosyl-(1-->3)-L-seryl-L-proline via removal of the N-carbobenzoxy group, followed by deacylation.

Carbohydrate Conformation↗
PubMed1985

Membrane stabilization during freezing: the role of two natural cryoprotectants, trehalose and proline.

The relative effectiveness of two natural cryoprotectants, proline and trehalose, in preserving membrane structure and function during freezing was studied. Isolated vesicles of sarcoplasmic reticulum (SR) from lobster muscle (Homarus americanus) were employed to study changes in structure and function during rapid freeze-thaw conditions. Both proline and trehalose were shown to effectively preserve the structure (assessed with freeze fracture) and function (assessed by the ability of the membranes to transport calcium) in the frozen vesicles. As a first step toward determining the mechanism of cryoprotection by these compounds, we have investigated their effectiveness in inhibiting freezing induced fusion between phospholipid vesicles. Pamiltoyloleoyl-phosphatidylcholine: phosphatidylserine (85:15 mole ratio) small unilamellar vesicles (SUVs) were made incorporating one of the following fluorescent probes, and energy donor, cholesteryl anthracene-9-carboxylate, or an energy acceptor, nitrobenzo-2-oxa-1,3-diazole phosphatidylethanolamine to investigate the amount of membrane mixing during rapid freeze-thaw cycles, and storage at -20 degrees C. Membrane mixing was measured as an energy transfer from donor to acceptor when donor vesicles and acceptor vesicles were mixed before a particular freezing treatment. Membrane mixing was correlated with structural changes in these membranes by freeze-fracture analysis. Both trehalose and proline were found to be more effective in preventing membrane mixing between SUVs than the standard protectants, glycerol and dimethylsulfoxide.

Animals↗
PubMed1986

Sodium-independent binding of L-[3H]proline to hippocampal synaptic membranes.

L-[3H]Proline binds specifically and saturably to rat hippocampal synaptic membranes in the absence of inorganic ions. Saturation isotherms constructed in Hepes-Tris buffer best fit a model of a single independent population of binding sites with a dissociation constant of 1.6 microM and maximum density of 16 pmol/mg protein. The rank order of displacement of radioligand by proline analogues suggests that binding sites of this type could be receptors responsible for proline-induced retinal spreading depression and inhibition of memory consolidation.

Animals↗
PubMed1991

A C-terminal proline is required for bioluminescence of the Ca(2+)-binding photoprotein, aequorin.

The requirement for a proline residue at the C-terminus of the Ca(2+)-binding photoprotein, aequorin, was investigated by measuring luminescence activities of a series of C-terminal deletion mutants, substitution mutants and an addition mutant. CD spectral measurements of apoaequorin with the C-terminal proline deleted showed a small change in secondary structure. In all cases studied, the C-terminal proline was required for bioluminescence activity.

Aequorin↗
PubMed1995

Effect of the C-terminal proline repeats on ordered packing of squid rhodopsin and its mobility in membranes.

Negative stain electron microscopy and saturation transfer electron spin resonance spectroscopy have been used to compare the lattice ordering and in-plane membrane mobility of full-length and C-terminally cleaved squid rhodopsin. The C-terminus of squid rhodopsin contains a negatively charged region followed by 9-10 repeats of a proline-rich sequence, not found in rhodopsins other than those of cephalopod invertebrates, but similar proline repeats are found in other, unrelated membrane proteins. We find that the proline repeats cluster the rhodopsins into small groups, interfering with two-dimensional crystallization and maintaining their mobility in the membrane.

Animals↗
PubMed1985

Interference by ethanol of coupling between gluconeogenesis and ureagenesis from proline in isolated hepatocytes.

Proline stimulated equally the production of glucose and urea by isolated hepatocytes. Ethanol suppressed glucose production much more strongly than urea synthesis. The proline-derived carbon not reaching glucose was found as lactate. Inhibition of phosphoenolpyruvate synthesis with 3-mercaptopicolinate blocked gluconeogenesis, but was without effect on lactate production. Acetate was formed from endogenous sources, as well as from ethanol. Its accumulation from ethanol was enhanced both by proline and lactate. The differential effect of ethanol on gluconeogenesis and ureagenesis appears to be related to its effect on the redox state of the cell.

Animals↗
PubMed1995

Alpha-methyl-proline restores normal levels of bone collagen Type I synthesis in ovariectomized rats.

Collagen type I is the major protein of bone matrix and significantly reduced in osteoporosis. We tested the effect of alpha - methyl - proline on collagen synthesis in the model of the ovariectomized rat. Collagen synthesis was studied at the transcriptional level using Northern and dot blotting and at the protein level using hydroxyproline determination and a specific dye binding collagen assay. Alpha - methyl- proline treatment significantly increased collagen synthesis as compared to untreated ovariectomized and estradiol treated ovariectomized rats and restored collagen synthesis to levels of sham operated rats. Proline analogues were described to stimulate procollagen synthesis at the transcriptional level, however, if incorporated, lead to negative collagen production due to rapid intracellular degradation of the deficient collagen. Our synthesized analogue is not being incorporated, thus not interfering with collagen conformation and can therefore induce collagen production.

Animals↗
PubMed1995

Isotopic evidence for the differential regulation of arginine and proline synthesis in man.

Arginine and proline derive from the metabolism of delta 1-pyrolline-5-carboxylate, a product of intestinal glutamic acid metabolism. We studied the extent of glutamate, arginine, and proline synthesis in four adult fed and fasted women. The subjects ingested a single dose of a mixture of uniformly (U)-13C-labeled amino acids and carbohydrate of algal origin. Frequent blood samples were taken for 24 hours. All the mass isotopomers of plasma lysine, glutamate + glutamine (GLX), arginine, and proline were measured using negative chemical ionization, selected-ion monitoring gas chromatography-mass spectrometry. In this isotopic approach, the appearance of U-13C-amino acid in the plasma reflects entry of the dietary amino acids, and the appearance of 13C in lower mass isotopomers demonstrates synthesis of the respective amino acids by the subject. All the mass isotopomers (including [M + 4]) of GLX became enriched with 13C. We suggest that the [M + 4] isotopomer of GLX reflects synthesis of the amino acid from alpha-ketoglutarate derived from the metabolism of U-13C-carbohydrate by the bacterial flora. Arginine labeling showed two patterns. The [M + 5] isotopomer of plasma arginine was labeled as rapidly as [M + 6] (ie, tracer) arginine, and we propose that the appearance of the [M + 5] isotopomer reflects the synthesis of citrulline from dietary [M + 5]-glutamate in first pass. The [M + 1] to [M + 3] isotopomers of arginine were also labeled for a prolonged period of time, suggesting that systemic glutamate was also a precursor for arginine synthesis.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1976

Reversions of two proline-requiring auxotrophs of Haemophilus influenzae by n-methyl-n'-nitro-n-nitrosoguanidine and hydrazine.

New mutation detection systems are described for Haemophilus influenzae. They involve two independently isolated proline auxotrophs which appear to be mutants at different sites in a proline locus (proB) that is very closely linked to a locus (thd) for thymidine requirement. One of the mutants, proB1, appears to revert to prototrophy only by mutations at the locus. The other, proB2, reverts both by mutation at the locus and by unlinked suppressors. The latter account for about 90% of the reversions induced by MNNG and by HZ. The close linkage of proB to thd was used to distinguish between true revertants and suppressors by a transformation test. A comparison was made between the mutation induction kinetics of the different classes of revertants and mutations to novobiocin resistance with MNNG and HZ. The very different induction kinetics for these two mutagens previously reported for the novobiocin resistance system were also found for the proline systems. There were some differences between the detection systems, however, in the frequency of induced mutation relative to the spontaneous frequency and, in one case, in the form of the induction curve. It is concluded that the major features of the induction curves reflect the amount of damage done to DNA and so are general for all systems, but that there are some features which are locus-or site-specific.

DNA, Bacterial↗
PubMed1995

Age-related alteration of proline hydroxylase and collagen-binding heat shock protein (HSP47) expression in human fibroblasts.

Changes in the expression of alpha and beta subunits of proline 4-hydroxylase (PH alpha and PH beta) and HSP47, implicated as a molecular chaperone specific for procollagen processing, were examined in human embryonal fibroblasts in relation to in vitro aging. For this purpose a model with treatments causing the decreased hydroxylation of proline residues in procollagens was used. In cells at a low population doubling level (PDL) induction of PH alpha, PH beta, and HSP47 by depletion of ascorbate or addition of alpha-alpha' dipyridyl could be clearly demonstrated by immunoprecipitation and Northern blotting. In contrast, the induction of PH alpha and HSP47 expression was markedly attenuated in high PDL cells, indicating an age-related decrease in response to procollagen retention in the ER caused by hypohydroxylation of proline residues of procollagens.

Animals↗