Search PubMed⌕ Search

SEARCH · Search PubMed

Results for “Precursor limitation”

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 145 records · Page 8Linked to original sources
PubMed2002

Metabolic and cardiorespiratory responses to "the lactate clamp".

To evaluate the hypothesis that precursor supply limits gluconeogenesis (GNG) during exercise, we examined training-induced changes in glucose kinetics [rates of appearance (R(a)) and disappearance (R(d))], oxidation (R(ox)), and recycling (R(r)) with an exogenous lactate infusion to 3.5-4.0 mM during rest and to pretraining 65% peak O(2) consumption (VO(2 peak)) levels during exercise. Control and clamped trials (LC) were performed at rest pre- (P(R)R, P(R)R-LC) and posttraining (P(O)R, P(O)R-LC) and during exercise pre- (P(R)E(X)) and posttraining at absolute (P(O)A(B), P(O)A(B)-LC) and relative (P(O)R(L), P(O)R(L)-LC) intensities. Glucose R(r) was not different in any rest or exercise condition. Glucose R(a) did not differ as a result of LC. Glucose R(ox) was significantly decreased with LC at P(O)R (0.38 +/- 0.03 vs. 0.56 +/- 0.04 mg. kg(-1). min(-1)) and P(O)A(B) (3.82 +/- 0.51 vs. 5.0 +/- 0.62 mg. kg(-1). min(-1)). Percent glucose R(d) oxidized decreased with all LC except P(O)R(L)-LC (P(R)R, 32%; P(R)R-LC, 22%; P(O)R, 27%; P(O)R-LC, 20%; P(O)A(B), 95%; P(O)A(B)-LC, 77%), which resulted in a significant increase in oxidation from alternative carbohydrate (CHO) sources at rest and P(O)A(B). We conclude that 1) increased arterial [lactate] did not increase glucose R(r) measured during rest or exercise after training, 2) glucose disposal or production did not change with increased precursor supply, and 3) infusion of exogenous CHO in the form of lactate resulted in the decrease of glucose R(ox).

Adolescent↗
PubMedDate not supplied

Mechanisms of ubiquitin-mediated, limited processing of the NF-kappaB1 precursor protein p105.

In most cases, target proteins of the ubiquitin system are completely degraded. In several exceptions, such as the first step in the activation of the transcriptional regulator NF-kappaB, the substrate, the precursor protein p105, is processed in a limited manner to yield the active subunit p50. p50 is derived from the N-terminal domain of p105, whereas the C-terminal domain is degraded. The mechanisms involved in this unique process have remained elusive. We have shown that a Gly-rich region (GRR) at the C-terminal domain of p50 is one important processing signal and that it interferes with processing of the ubiquitinated precursor by the 26S proteasome. Also, amino acid residues 441-454 are important for processing under non-stimulated conditions. Lys 441 and 442 serve as ubiquitination targets, whereas residues 446-454 may serve as a ligase recognition motif. Following IkappaB kinase (IKK)-mediated phosphorylation, the C-terminal domain of p105, residues 918-934, recruits the SCF(beta-TrCP) ubiquitin ligase, and ubiquitination by this complex leads to accelerated processing. The two sites appear to be recognized under different physiological conditions by two different ligases, targeting two distinct recognition motifs. We have shown that ubiquitin conjugation and processing of a series of precursors of p105 that lack the C-terminal IKK phosphorylation/TrCP binding domain, is progressively inhibited with increasing number of ankyrin repeats. Inhibition is due to docking of active NF-kappaB subunits to the ankyrin repeat domain in the C-terminal half of p105 (IkappaBgamma). Inhibition is alleviated by phosphorylation of the C-terminal domain that leads to ubiquitin-mediated degradation of the ankyrin repeat domain and release of the anchored subunits. We propose a model that may explain the requirement for two sites: a) a basal site that may be involved in co-translational processing prior to the synthesis of the ankyrin repeat domain; and b) a signal-induced site that is involved in processing/degradation of the complete molecule following cell activation, with rapid release of stored, transcriptionally active subunits.

Amino Acid Motifs↗
PubMed1985

T lymphocyte function during experimental Chagas' disease: production of and response to interleukin 2.

Infection of mice with Trypanosoma cruzi results in a severe immunosuppression, accompanied by the appearance of autoimmune symptoms. We have previously shown that proliferation and interleukin 2 production by concanavalin A-stimulated T cells from infected mice is severely depressed. In this study we show that at least two phenomena are responsible for this depression. First, mixing experiments showed the existence, in spleens of infected animals, of adherent, Thy-1-negative and radioresistant suppressor cells. Second, studies of enriched T cell populations and analysis of precursors by limiting dilution showed that the T cell compartment itself was impaired in infected animals: responses of enriched T cells, even when reconstituted with normal accessory cells, reached only 40% of those obtained with normal uninfected mice.

Animals↗
PubMed1987

Role of glandular kallikreins as growth factor processing enzymes: structural and evolutionary considerations.

Hormones and growth factors are generally released from larger precursors by limited proteolysis. The causative agents remain poorly defined with respect to location and properties. One subset of proteases, the glandular kallikreins, have been implicated in a few cases, in part because of their specific association with mature forms of some hormones. However, limited distribution and low copy number in some species cast doubt on this hypothesis, and they may well play other physiological functions that remain to be elucidated.

Amino Acid Sequence↗
PubMed2000

Decreased hippocampal metabolic activity in Alzheimer patients is not reflected in the immunoreactivity of cytochrome oxidase subunits.

In the present study we have compared histochemically determined cytochrome oxidase activity with the levels of immunocytochemically stained cytochrome oxidase subunits (CO II and CO IV) and ATP synthase in the human hippocampus in relation with Alzheimer's disease. Cytochrome oxidase activity was significantly reduced in all hippocampal areas of Alzheimer patients. The protein levels of subunits II and IV were not different between control subjects and Alzheimer patients. Additionally, it was observed that the active cytochrome oxidase is evenly distributed over both cell bodies and neuropil, while a relatively large pool of inactive enzyme or precursors is limited to the neuronal somata. Further, in Alzheimer patients the CO IV immunoreactivity decreased with age, whereas in control subjects it increased with age. Our results suggest that the assembly of cytochrome oxidase or the processing of its subunits may be impaired.

Aged↗
PubMed1997

In vivo longitudinal analysis of a dominant TCR repertoire selected in human response to influenza virus.

Recent studies have demonstrated biased usage of TCR V beta 17 and a high degree of diversity in J beta usage within the influenza virus matrix epitope (M.58-66)-specific CTL response. In contrast, in the course of a study on the cellular response to influenza A virus, we found preferential usage of V beta 17-J beta 2.2 rearrangement in an individual with an unexpectedly high number of CTL precursors (CTLp). We took advantage of such situation to study the longitudinal repertoire of the CD8+ T cell precursors. By limiting dilution analysis combined with the use of a clonotypic primer corresponding to the CDR3 region of this matrix-specific TCR V beta chain, the influenza-specific CTLp were shown to be stable for a period of 6 years. Overall, our results show that virus-specific CTLp can be directly monitored in vivo by molecular fingerprinting without in vitro restimulation. These findings might be extremely important for evaluation of the specific immune response to a given human pathogen.

Animals↗
PubMedDate not supplied

Protein-DNA interactions during phenotypic differentiation.

We have been studying the molecular mechanism of neuronal differentiation through which the multipotent precursor becomes limited to the final transmitter phenotype. Here we focused on the role of the 5' proximal regulatory cassette (-190; +53 bp) of the rat enkephalin (rENK) gene in the developmental regulation of the enkephalin phenotype. Several well characterized cis-elements, including AP2, CREB, NF1, and NFkB, reside on this region of the rENK gene. These motifs were sufficient to confer activity-dependent expression of the gene during neurodifferentiation when it was tested using transient transfection assays of primary developing spinal cord neurons treated with tetrodotoxin (TTX). This region was then used as a DNA probe in mobility shift assays, with nuclear proteins derived from phenotypically and ontogenetically distinct brain regions. Only a few low abundance protein-DNA complexes were detected and only with nuclear proteins derived from developing but not from adult brain. The spatiotemporal pattern of these complexes did not show correlation with enkephalin expression which was assessed by RT-PCR. We employed synthetic probes corresponding to consensus as well as ENK-specific sequences of the individual motifs to identify the nature of the observed bands. Although both consensus NF1 and enkCRE1(NF1) formed complexes with nuclear proteins derived from the striatum and cortex at various ages, the appearance of the bands was not correlated with ENK expression. Surprisingly, no complexes were detected if other ENK-specific motifs were used as probes. We also tested nuclear extracts derived from forskolin-induced and control C6 glioma cells, again using the whole proximal regulatory cassette as well as individual motifs. These experiments showed the formation of elaborate protein-DNA bands. There was no direct correlation between the appearance of bands and forskolin-induced ENK expression. Unexpectedly, all ENK-specific motifs formed specific and highly abundant protein-DNA complexes when nuclear extracts from the human tumor cell line (HeLa), which does not express ENK, were used. Based on these observations, we concluded that: 1. Interactions between the proximal regulatory cassette and additional probably far distant regions of the rENK gene and their binding proteins may be necessary to confer developmentally regulated, cell-specific expression of the ENK gene; and 2. Inducibility of the gene by common cis-elements can be governed by this region; however, the cell-specificity of the induction remains elusive.

Animals↗
PubMed2007

L-tyrosine production by deregulated strains of Escherichia coli.

The excretion of the aromatic amino acid L: -tyrosine was achieved by manipulating three gene targets in the wild-type Escherichia coli K12: The feedback-inhibition-resistant (fbr) derivatives of aroG and tyrA were expressed on a low-copy-number vector, and the TyrR-mediated regulation of the aromatic amino acid biosynthesis was eliminated by deleting the tyrR gene. The generation of this L: -tyrosine producer, strain T1, was based only on the deregulation of the aromatic amino acid biosynthesis pathway, but no structural genes in the genome were affected. A second tyrosine over-producing strain, E. coli T2, was generated considering the possible limitation of precursor substrates. To enhance the availability of the two precursor substrates phosphoenolpyruvate and erythrose-4-phosphate, the ppsA and the tktA genes were over-expressed in the strain T1 background, increasing L: -tyrosine production by 80% in 50-ml batch cultures. Fed-batch fermentations revealed that L: -tyrosine production was tightly correlated with cell growth, exhibiting the maximum productivity at the end of the exponential growth phase. The final L: -tyrosine concentrations were 3.8 g/l for E. coli T1 and 9.7 g/l for E. coli T2 with a yield of L: -tyrosine per glucose of 0.037 g/g (T1) and 0.102 g/g (T2), respectively.

Biotechnology↗
PubMed1993

Potential bioactivated neurotoxicants, N-methylated beta-carbolinium ions, are present in human brain.

Potential bioactivated neurotoxicants, 2-N-methyl-beta-carbolinium and 2,9-N,N'-dimethyl-beta-carbolinium ions, as well as N-methylation activities which form these charged species, were analyzed for the first time in the parietal association cortex and the substantia nigra of human brain using GC/MS and HPLC. The brains were taken during forensic autopsies from corpses without obvious degeneration of substantia nigra. In the cortex, 2-methyl-norharmanium ion (2-MeNH) and 2,9-dimethyl-norharmanium ion (2,9-Me2NH) were detected in almost all samples. 2-Methyl-harmanium ions (2-MeHA) and 2,9-dimethyl-harmanium ions (2,9-Me2HA) were detectable in only two samples. In substantia nigra samples pooled from 3 or 4 brains for analysis, 2-MeNH and 2,9-Me2NH levels were higher than those in the cortex, whereas 2-MeHA and 2,9-Me2HA were below detection limits. Their precursors, norharman (NH) and harman (HA), were also measured using HPLC/fluorescence detection. In both regions, NH and HA were present in almost all samples; levels of NH and HA were also significantly higher in the nigra than in the cortex. Using 9-methyl-NH and 2-MeNH as substrates, in vitro N-methylation of the 2[beta] and 9[indole] nitrogens toward beta-carbolines was measured both in the cortex and in the nigra. 2[beta]-N-Methylation activity was significantly higher than 9[indole]-N-methylation activity in both regions. Recent studies show that beta-carbolinium ions resemble the synthetic parkinsonian toxicant, MPP+, with respect to structure and neurotoxic activity. Such 'bioactivated' carbolinium ions could be endogenous causative factors in Parkinson's disease.

Brain Chemistry↗
PubMed1985

Are any functionally mature cells of medullary phenotype located in the thymus cortex?

Experiments were undertaken to test if thymocytes of "mature" or "medullary" phenotype were restricted to the medullary area of the thymus. A calculation based on direct cell counts on serial sections indicated that 11.5% of adult male CBA thymic lymphoid cells were within the medullary zone. Since only 3-4% of thymocytes were cortisone resistant, the majority of thymocytes within the medulla were, like cortical thymocytes, cortisone sensitive. A series of cell surface antigenic markers, used alone or in pairs, suggested that 13-15% of thymocytes were of medullary phenotype, somewhat more than the number of thymocytes actually present in the medulla. However, much of this discrepancy could be explained by differential death of cortical cells during isolation and staining, and by the existence in the cortex of a subpopulation of early blast cells which shared some, but not all markers with medullary thymocytes. A direct test for mature or medullary phenotype cells in the cortex involved selective transcapsular labeling of outer-cortical cells with fluorescent dyes, followed by multiparameter immunofluorescent analysis of the 10% labeled population. Outer-cortical thymocytes included some cells (mainly early blasts) sharing some markers with medullary thymocytes, but very few (less than 1%) of these cells expressed all the characteristic "mature" markers. Limit-dilution precursor frequency studies showed the level of functional cells in the outer cortex was extremely low. The overall conclusion was that the vast majority of cells of complete "mature" phenotype are confined to the thymic medulla. These findings favor the view that thymus migrants originate from the thymic medulla, but do not exclude a cortical origin. The results also illustrate the need for multiparameter analysis to distinguish medullary thymocytes from early blast cells.

Animals↗
PubMed1996

Distinctive aspects of metabolism and nutrition in infancy.

OBJECTIVES: The effects of genes, the stage of development, and the environment on various metabolic processes in infancy are described. Some themes discussed cross these three boundaries. CONCLUSIONS: Certain substances not normally regarded as essential may become conditionally essential if their precursors are limited in the diet or, alternatively, if the processes of conversion are reduced in activity because of abnormal gene function, or developmental immaturity. Diet is a clear environmental influence but, because the nature of the diet is closely related to age, it is a developmental influence as well. Certain nutrients are followed from the diet, via the gut and intermediary metabolism through to individual tissues and the whole body. The relationships of diet, metabolism and brain function have attracted considerable investigation in recent years. In the right environment, with the correct genes, the processes of development will be smooth and without undue metabolic disturbance. Considerable variation can be accommodated within the elasticity of the systems, but some changes may lead to temporary, or even permanent, malfunction.

Child Development↗
PubMed1989

Enhanced high energy phosphate recovery with ribose infusion after global myocardial ischemia in a canine model.

High energy phosphate levels are depressed following global ischemia and require several days to completely recover. Short-term methods to enhance ATP recovery have included infusion of ATP precursors, inhibition of enzymes that catabolize AMP, and membrane transport stabilization. Several precursors have been used to augment adenine nucleotide synthesis including adenosine, inosine, adenine, and ribose. Because of the short-term nature of previous experiments, recovery had been incomplete and the effects in the intact animal unknown. The purpose of this study was to determine the effects of ribose infusion in a long-term model of global ischemia and attempt to identify the precursor which limits myocardial ATP regeneration in the intact animal. Global myocardial ischemia (20 min, 37 degrees C) was produced in dogs on cardiopulmonary bypass. With reperfusion either ribose (80 mM) in normal saline or normal saline alone was infused at 1 ml/min into the right atrium and the animals were followed for 24 hr. Ventricular biopsies were obtained through an indwelling ventricular cannula prior to ischemia, at the end of ischemia, and 4 and 24 hr postischemia and analyzed for adenine nucleotides and creatine phosphate levels. Radiolabeled microspheres were used to measure myocardial and renal blood flows and no significant difference was found between ribose-treated control groups. In both groups, myocardial ATP levels fell by at least 50% at the end of ischemia. No significant ATP recovery occurred after 24 hr in the control dogs, but in the ribose-treated animals, ATP levels rebounded to 85% of control by 24 hr.(ABSTRACT TRUNCATED AT 250 WORDS)

Adenosine Triphosphate↗
PubMed1988

A subpopulation of cultured avian neural crest cells has transient neurogenic potential.

Neural crest cells of vertebrate embryos produce neurons, glia, pigment cells, and connective tissue in vivo and in vitro. To test the developmental potential of apparently undifferentiated crest cells, we have used the monoclonal antibody A2B5, which recognizes a cell surface glycolipid characteristic of neurons, to identify and immunoablate a subpopulation of cultured avian neural crest cells with a neuronal phenotype. Our results indicate that a limited neurogenic precursor subpopulation is present in cultures of avian neural crest cells and that the fate of this subpopulation can be influenced by environmental conditions arising when dispersal of neural crest cells is delayed.

Animals↗
PubMed1996

Is there a neural stem cell in the mammalian forebrain?

Neural precursor cells have been of interest historically as the building blocks of the embryonic CNS and, most recently, as substrates for restorative neurological approaches. The majority of previous in vitro studies of the regulation of neural-cell proliferation by polypeptide growth factors, and in vivo studies of neural lineage, argue for the presence of precursors with limited proliferative or lineage potential in the mammalian CNS. This is in contrast to renewable tissues, such as the blood or immune system, skin epithelium and epithelium of the small intestinal crypts, which contain specialized, self-renewing cells known as stem cells. However, recent in vitro and in vivo studies from our and other laboratories lead us to conclude that neural stem cells, with self-renewal and multilineage potential, are present in the embryonic through to adult mammalian forebrain.

Animals↗
PubMed1996

Analogues of 10-deazaaminopterin and 5-alkyl-5,10-dideazaaminopterin with the 4-substituted 1-naphthoyl group in the place of 4-substituted benzoyl.

10-Deaza modifications of classical antifolate analogues bearing the 1,4-disubstituted naphthalene ring in place of the 1,4-disubstituted benzene ring were prepared and tested for antitumor activity. Naphthalene analogues (9a-c, respectively) of 10-deazaaminopterin, 5-methyl-5, 10-dideazaaminopterin, and 5-ethyl-5,10-dideazaaminopterin were prepared by a route consisting of C-alkylations of the anion derived from 4-carboxyl-1-naphthaleneacetic acid dimethyl ester (2) by 6-(bromomethyl)-2,4-diaminopteridine (1a) and 6-(bromomethyl)-2,4-diamino-5-methyl- and -5-deazapteridines (1b and 1c, respectively) followed by ester hydrolysis and subsequent decarboxylation to give naphthalene analogues (7a-c, respectively) of 4-amino-4-deoxy-10-deazapteroic acid and 4-amino-4-deoxy-5- methyl- and -5-ethyl-5,10-dideazapteroic acids. Peptide coupling of 7a-c with L-glutamic acid dialkyl ester followed by mild ester hydrolysis gave target compounds 9a-c. The key advantage of this route is circumvention of a hydrogenation step requiring selectivity as in earlier approaches involving 9,10-olefinic precursors. Steric limitations thwarted plans to prepare the naphthalene analogue of 10-ethyl-10-deazaaminopterin; attempted alkylations of 2-(4-carboxy-1-naphthyl)butyric acid dimethyl ester with 1a failed as did attempted further alkylation (by EtBr) of the product derived from 1a and 2. Growth inhibition tests against three tumor cell lines (L1210, S180, and HL60) showed 9a to be 4-6-fold more inhibitory than methotrexate but not as inhibitory as 10-ethyl-10-deazaaminopterin; 9b and 9c were no more inhibitory than MTX. In tests against the EO771 mammary adenocarcinoma in mice, 9a was less active than MTX.

Adenocarcinoma↗
PubMed1968

Effect of growth hormone on ribonucleic acid metabolism. The template activity of the chromatin and molecular species of ribonucleic acid synthesized after treatment with the hormone.

Growth hormone stimulates the synthesis of RNA in hypophysectomized rat liver. The question whether the hormonal stimulation of RNA synthesis is due to the activation of repressed cistrons or to other factors was studied. Nuclear RNA from the livers of adult female hypophysectomized and growth-hormone-treated rats was examined for molecular homology by hybridization techniques: no new species of RNA were detected after hormone treatment. The template activity of the chromatin for RNA synthesis is also not increased by the action of growth hormone. Short- and long-pulse-labelling experiments demonstrate that the hormonal stimulation of RNA synthesis is most marked in experiments where the period of incorporation of radioactive precursors is limited to 1-2hr. It is concluded that the hormone influences essentially the rate of RNA synthesis in these tissues.

Animals↗
PubMed1998

Induction of nitric oxide synthase and nitric oxide-mediated apoptosis in neuronal PC12 cells after stimulation with tumor necrosis factor-alpha/lipopolysaccharide.

Exposure of neuronal PC12 cells, differentiated by nerve growth factor, to tumor necrosis factor-alpha (TNF-alpha) and bacterial lipopolysaccharide (LPS) resulted in de novo synthesis of inducible nitric oxide synthase (iNOS) mRNA and protein with an increase up to 24 h. Brain NOS expression was unaffected. The induction of iNOS in differentiated PC12 cells was associated with cell death characterized by features of apoptosis. The NOS inhibitors N-monomethylarginine, aminoguanidine, and 2-amino-5,6-dihydro-6-methyl-4H-1,3-thiazine.HCl prevented TNF-alpha/LPS-induced cell death and DNA fragmentation, suggesting that the TNF-alpha/LPS-induced cell death is mediated by iNOS-derived NO. This hypothesis is supported by the finding that addition of L-arginine, which serves as a precursor and limiting factor of enzyme-derived NO production, potentiated TNF-alpha/LPS-induced loss of viability.

Animals↗
PubMed2001

High-level HIV-1 viremia suppresses viral antigen-specific CD4(+) T cell proliferation.

In chronic viral infections of humans and experimental animals, virus-specific CD4(+) T cell function is believed to be critical for induction and maintenance of host immunity that mediates effective restriction of viral replication. Because in vitro proliferation of HIV-specific memory CD4(+) T cells is only rarely demonstrable in HIV-infected individuals, it is presumed that HIV-specific CD4(+) T cells are killed upon encountering the virus, and maintenance of CD4(+) T cell responses in some patients causes the restriction of virus replication. In this study, proliferative responses were absent in patients with poorly restricted virus replication although HIV-specific CD4(+) T cells capable of producing IFN-gamma were detected. In a separate cohort, interruption of antiretroviral therapy resulted in the rapid and complete abrogation of virus-specific proliferation although HIV-1-specific CD4(+) T cells were present. HIV-specific proliferation returned when therapy was resumed and virus replication was controlled. Further, HIV-specific CD4(+) T cells of viremic patients could be induced to proliferate in response to HIV antigens when costimulation was provided by anti-CD28 antibody in vitro. Thus, HIV-1-specific CD4(+) T cells persist but remain poorly responsive (produce IFN-gamma but do not proliferate) in viremic patients. Unrestricted virus replication causes diminished proliferation of virus-specific CD4(+) T cells. Suppression of proliferation of HIV-specific CD4(+) T cells in the context of high levels of antigen may be a mechanism by which HIV or other persistently replicating viruses limit the precursor frequency of virus-specific CD4(+) T cells and disrupt the development of effective virus-specific immune responses.

CD4-Positive T-Lymphocytes↗