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Biomedical subjects

L J Chen

Publications and source records attributed to L J Chen.

At least 55 records · Page 3Linked to original sources
PubMed1998

A mutant deficient in the plastid lipid DGD is defective in protein import into chloroplasts.

Most proteins in chloroplasts are encoded by the nuclear genome and synthesized in the cytosol with N-terminal extensions called transit peptides. Transit peptides function as the import signal to chloroplasts. The import process requires several protein components in the envelope and stroma and also requires the hydrolysis of ATP. Lipids have been implicated in the import process based on theories or experiments with in vitro model systems. We show here that chloroplasts isolated from an Arabidopsis mutant deficient in the plastid lipid digalactosyl diacylglycerol (DGD) were normal in importing a chloroplast outer membrane protein, but were defective in importing precursor proteins targeted to the interior of chloroplasts. The impairment includes the binding, or docking, step of the import process that is supported by 100 microM ATP.

Adenosine Triphosphate↗
PubMed1998

Genomic cloning of 18 kDa oleosin and detection of triacylglycerols and oleosin isoforms in maturing rice and postgerminative seedlings.

Oleosins are hydrophobic proteins localized abundantly in the oil bodies of plant seeds. Two distinct oleosin isoforms of molecular masses 18 and 16 kDa are present in rice oil bodies. These isoforms were found in similar ratio in rice embryos and aleurone layers. To survey potential DNA sequences involved in the activation of oleosin genes, a genomic clone of rice 18 kDa oleosin was sequenced, and its 5'-flanking region was compared with that of the known rice 16 kDa oleosin gene. Corresponding mRNAs of the two rice oleosin isoforms appeared seven days after pollination and vanished in mature seeds. Triacylglycerols and oleosins were accumulated concomitantly in maturing rice reeds in accord with the active assembly of oil bodies, and partly mobilized in postgerminative seedlings. Approximately 60% of the stored triacylglycerols in rice were not utilized: while the majority of oil bodies in embryos were mobilized in five days after imbibition, those in aleurone layers remained intact in postgerminative seedlings.

Base Sequence↗
PubMed1998

Oncocytic adenomatous hyperplasia of the lacrimal sac: a case report and review of the literature.

Oncocytic tumors of the lacrimal sac are very rare, with only 21 cases documented in the world literature. The authors report a 75-year-old woman who sought treatment for recurrent dacryocystitis and a palpable mass in the left medial canthal area. The patient underwent surgery for removal of a suspected lacrimal sac cancer, but pathologic findings indicated benign oncocytic adenomatous hyperplasia. Complete removal of the tumor and long-term follow-up are necessary in patients with lacrimal sac oncocytic lesions. The authors discuss the characteristic features of ocular adnexal oncocytic lesions and review the literature.

Adenocarcinoma↗
PubMed1997

Identification of the transcription start site for the spinach chloroplast serine tRNA gene.

Deleting part of the 3' end of the spinach chloroplast serine tRNA coding region, which destroyed the proper folding of its RNA transcript and resulted in the inhibition of tRNA processing, allowed the detection of a serine tRNA primary transcript. The transcription start site for this primary transcript, synthesized from the internal promoter, was mapped to -12 upstream from the mature tRNA coding region. Transcription analysis with various 5' deletion mutants suggested that the AT-rich region between -31 and -11, immediately upstream of the serine tRNA transcription start site, affects the transcription efficiency, and possibly the selection of transcription start site. Identification of the transcription start site for the spinach chloroplast serine tRNA gene in this study represents the first example of 5' end mapping of a tRNA precursor transcribed from chloroplast tRNA genes containing an internal promoter.

Base Sequence↗
PubMed1997

GTP regulation of (-)-stepholidine binding to R(H) of D1 dopamine receptors in calf striatum.

(-)-Stepholidine (SPD) exhibits antagonist effects on normosensitive dopamine (DA) receptors, but it has an agonist action on rotation in unilaterally 6-hydroxydopamine (6-OHDA)-lesioned rats. The present work endeavors to further elucidate the mechanism of its agonist action on D1 receptors. [3H]R(+)-7-chloro-8-hydroxy-3-methyl-1-phenyl-2,3,4,5-tetrahydro-1H-3-be nzazepine ([3H]SCH-23390) and [3H]spiperone were used, respectively, as radioligands in D1 and D2 DA receptor binding assays in calf striatal membranes. Experimental data were analyzed by a non-linear regression computer program, GraphPAD InPlot 3.15. The competition curves were fitted first by a single-site equation and then by a two-site equation. The results showed that both apomorphine (APO) and SPD competitively inhibited [3H]SCH-23390 binding. Their competition curves fitted best to the two-site equation (P < 0.05) with a high-affinity site (R(H)) and a low-affinity site (R(L)) to DA receptors. The K(H) and K(L) values (nM) were 2.7 +/- 0.45 and 378 +/- 62 for APO, and 3.9 +/- 2.2 and 126 +/- 25 for SPD, respectively. In contrast, the competition curve of SCH-23390, a selective D1 DA receptor antagonist, fitted best to a single-site model with a Ki value of 1.7 +/- 0.5 nM. The R(H) of APO or SPD could be decreased by the addition of 450 microM GTP. In the [3H]spiperone binding test, the APO curve was modeled best by the two-site equation, while the SPD curve fitted best to a single-site model. In the rotational behavior test, APO induced 441 +/- 20 turns/30 min in the 6-OHDA-lesioned rats, and SPD induced 310 +/- 42 turns/30 min, while SCH-23390 antagonized the SPD-induced rotation but did not induce rotational behavior. These results suggest that SPD possesses agonist actions on D1 but antagonist effects on D2 DA receptors.

Adenylyl Cyclases↗
PubMed1997

A novel chloroplastic outer membrane-targeting signal that functions at both termini of passenger polypeptides.

Several components in the machinery mediating the import of nuclear-encoded chloroplastic precursor proteins have been identified. One of the components, OEP34, is an outer membrane protein and is synthesized at its mature size in the cytosol without a distinguishable chloroplast-targeting signal. To address the question of how components in the transport machinery are imported to chloroplasts themselves, we first identified the chloroplastic outer membrane-targeting signal of OEP34. Using an Arabidopsis homologue of the originally isolated pea OEP34, we show that the outer membrane-targeting signal of OEP34 is located within a 10-amino acid hydrophobic core of the C-terminal membrane anchor. Interestingly, this signal can target a passenger protein to the chloroplastic outer membrane no matter whether it is placed at the N or C terminus of a passenger protein. Proper insertion of fusion proteins into the outer membrane requires in addition the C-terminal hydrophilic region following the hydrophobic core. Furthermore, passenger proteins fused to the C terminus of the targeting/insertion signal were most likely imported into the intermembrane space of the envelope.

Amino Acid Sequence↗
PubMed1997

Transcription and processing of the gene for spinach chloroplast threonine tRNA in a homologous in vitro system.

An in vitro system was established to study the transcription and processing of threonine tRNA using spinach chloroplast enzyme extract. Experiments using a series of 5' deletion mutants demonstrated that the transcription of trnT gene required no 5' upstream promoter elements. Four plasmid DNA templates containing trnT were constructed for tRNA processing assay. The processing reaction was carried out either with exogenously added precursor-tRNAs made by T7 RNA polymerase or with RNAs synthesized by the transcription activity in the same processing enzyme extract. Both assays demonstrated that the 5' and 3' ends of mature tRNA were processed endonucleolytically and the processing of the 5' end preceded the maturation of the 3' end. The activity of nucleotidyl transferase that adds CCA nucleotides to the 3' end of tRNA was also observed. The use of a coupled transcription and processing system provides us with a better insight to the tRNA processing mechanism of the chloroplast.

Base Sequence↗
PubMed1997

Dual actions of (-)-stepholidine on the dopamine receptor-mediated adenylate cyclase activity in rat corpus striatum.

(-)-Stepholidine (SPD) is an antagonist of normosensitive dopamine (DA) receptors, but it exhibits D1 agonistic action on rotational behaviour in rats with unilateral 6-hydroxydopamine (6-OHDA) lesions of the substantia nigra pars compacta (SNC). In the present study, agonistic and antagonistic effects of SPD on the DA receptor-mediated synaptosomal adenylate cyclase (AC) activity in rat striatum were investigated. After blockade of D2 receptors, SPD augmented AC activity dose-dependently. The EC50 value was 41.1 +/- 8.6 micromol/L. At the concentration of 10 micromol/L, SPD increased cAMP formation from a basal level (50.8 +/- 10.3 pmol/mg protein/min) to 133.7 +/- 31.8 pmol/mg protein/min. The SPD-induced stimulation of AC activity was almost completely reversed by 10 micromol/L Sch23390. These results indicate that SPD possesses an agonistic action on the D1 receptor. Forskolin-stimulated adenylate cyclase (FSAC) activity was used as a model to elucidate the effect of SPD on D2 receptors. The results indicate that DA inhibited FSAC activity dose-dependently, while SPD partially restored FSAC activity. Taken together, these results support the conclusion that SPD has dual actions on DA receptors that mediate AC activity, i.e., an agonistic action on D1 receptors and an antagonistic action on D2 receptors.

Adenylyl Cyclase Inhibitors↗
PubMed1997

Characterization of amino acid and glutathione adducts of cis-2-butene-1,4-dial, a reactive metabolite of furan.

Metabolic activation of the hepatocarcinogen furan yields metabolites that react covalently with proteins. cis-2-Butene-1,4-dial is a microsomal metabolite of furan. This reactive aldehyde is thought to be the toxic metabolite that is responsible for the carcinogenic activity of furan. In order to characterize the chemistry by which this unsaturated dialdehyde could alkylate proteins, the products formed upon reaction of cis-2-butene-1,4-dial with model nucleophiles in pH 7.4 buffer were investigated. N(alpha)-Acetyl-L-lysine (AcLys) reacts with cis-2-butene-1,4-dial to form N-substituted pyrrolin-2-one adducts. N-Acetyl-L-cysteine (AcCys) reacts rapidly with cis-2-butene-1,4-dial to form multiple uncharacterized products. The inclusion of AcLys in this reaction mixture yielded an N-substituted 3-(S-acetylcysteinyl)pyrrole adduct which links the two amino acid residues. Related compounds were isolated when cis-2-butene-1,4-dial and glutathione (GSH) were combined. In this case, cis-2-butene-1,4-dial cross-linked two molecules of GSH resulting in either cyclic or acyclic adducts depending on the relative GSH concentration. Incubation of furan with rat liver microsomes in the presence of [glycine-2-3H]GSH led to the formation of radioactive peaks that coeluted with synthetic standards for the bisgluthathione conjugates. These studies demonstrate that the reactive cis-2-butene-1,4-dial formed during the microsomal oxidation of furan reacts rapidly and completely with amino acid residues to form pyrrole and pyrrolin-2-one derivatives. Therefore, this metabolite is a likely candidate for the activated furan derivative that binds to proteins. The ease with which cis-2-butene-1,4-dial cross-links amino acids suggests that pyrrole-thiol cross-links may be involved in the toxicity observed following furan exposure.

Aldehydes↗
PubMed1997

Cantrell's syndrome in an infant.

Cantrell's syndrome is a rare combination of congenital midline thoracoabdominal defects and congenital heart disease. surgical repair can correct many of the anomalies. We report a neonate who presented with a short sternum, defective upper abdominal muscle, ectopic umbilicus, anterior diaphragmatic defect, ventricular septal defect and an intra-abdominal left ventricular diverticulum. Initially, the infant was treated with digoxin and diuretics for 5 months. Due to poor control of heart failure, one-stage surgical correction was performed with patch repair of the ventricular septal defect, ligation of left ventricular diverticulum and closure of the defects of the diaphragm and upper abdominal wall.

Abnormalities, Multiple↗
PubMed1996

Prospective study of noise exposure during pregnancy on birth weight.

To examine the effect of noise exposure during pregnancy on infant birth weight, a well-characterized cohort of 200 pregnant women in the first trimester participating in prenatal care clinics was followed throughout gestation (in Taiwan, 1991). Individual 24-hour noise exposure of all women was prospectively measured, and information regarding possible noise exposure from traffic and occupation was also obtained. Noise exposure during pregnancy was correlated with the birth weights of the women's babies. No association between personal noise exposure measured in decibels (less than 85 dBALeq during pregnancy) and birth weight was found. Possible occupational noise exposure (indicated by working in a manual job), traffic noise exposure (indicated by distance between the home and main streets), and a history of listening to amplified music and using personal listening devices during pregnancy also showed no effect on infant birth weight. Maternal weight, maternal weight gained during pregnancy, gestational age, and infant's sex were the four factors that correlated significantly with birth weight. The noise exposure experienced by women during pregnancy may not be great enough to affect their infants' birth weight.

Adolescent↗
PubMed1996

Protein targeting and integration signal for the chloroplastic outer envelope membrane.

Most proteins in chloroplasts are encoded by the nuclear genome and synthesized in the cytosol. With the exception of most quter envelope membrane proteins, nuclear-encoded chloroplastic proteins are synthesized with N-terminal extensions that contain the chloroplast targeting information of these proteins. Most outer membrane proteins, however, are synthesized without extensions in the cytosol. Therefore, it is not clear where the chloroplastic outer membrane targeting information resides within these polypeptides. We have analyzed a chloroplastic outer membrane protein, OEP14 (outer envelope membrane protein of 14 kD, previously named OM14), and localized its outer membrane targeting and integration signal to the first 30 amino acids of the protein. This signal consists of a positively charged N-terminal portion followed by a hydrophobic core, bearing resemblance to the signal peptides of proteins targeted to the endoplasmic reticulum. However, a chimeric protein containing this signal fused to a passenger protein did not integrate into the endoplasmic reticulum membrane. Furthermore, membrane topology analysis indicated that the signal inserts into the chloroplastic outer membrane in an orientation opposite to that predicted by the "positive inside" rule.

Amino Acid Sequence↗
PubMed1996

Effects of benzylpenicillin on glucose utilization, macromolecule synthesis and cell wall proteins of Listeria monocytogenes.

When growing cells were incubated in the presence of 100 ppm benzylpenicillin (BP) for 30 min and then harvested for metabolic studies, the initial rate of glucose utilization by resting cells was reduced by 19.6% compared to control cells, whereas the rates of protein, DNA and RNA synthesis were reduced by 40.7%, 55.0% and 87.5% respectively. Growth in the presence of 100 ppm BP for 2 h was found to result in a marked depletion of cell wall proteins.

Bacterial Proteins↗
PubMed1996

[A prevalence study on HBV and HCV infection status in patients with hemopathy].

A prevalence study on Hepatitis B virus (HBV) and Hepatitis C virus (HCV) infection in 144 patients with hemopathy was carried out, using an enzyme linked immunosorbent assay (ELISA). The HBsAg, HBcAb and anti-HCV positive rates in sera of these patients were 9.72%, 36.81% and 24.31% respectively, comparing with data from healthy control subjects, 12.03%, 46.30% and 0.93% respectively. No correlation between HCV infection and patient's age or sex was noticed. Nevertheless the incidence of HCV infection was closely related to the history and the frequency of blood transfusion. The ALT level in sera of patients with HCV infection was higher than that of patients without HCV infection. The ALT level in sera was the highest in patients superinfected with HBV and HCV. Our results suggested that blood transfusion and receiving blood products were important routes of HCV transmission in patients with hemopathy.

Adolescent↗
PubMed1996

[Effect of (+/-)12-chloroscoulerine on brain dopamine receptors].

AIM: To assess potencies of tetrahydroprotoberberines (THPB) and hydrobenzyltetrahydroisoquinolines (HBTI) on DA receptors. METHODS: The receptor binding assay with calf striatum to D1 and D2 receptors, and the animal behavior tests were used. RESULTS: (+/-) 12-Chloroscoulerine (CSL) was the most potent one among the THPB and HBTI. The affinities of CSL to D1 and D2 receptors were 13 and 51 nmol.L-1, respectively. In rats, CSL showed an antagonistic effect on the stereotypy and induced catalepsy. In the 6-OHDA lesioned rats, however, CSL exerted the agonistic effect to DA receptors. CONCLUSION: CSL had dual actions to DA receptors and its effects were similar to that of (-)stepholidine.

Animals↗
PubMed1996

[Antagonism of l-stepholidine against bromocriptine-inhibition on prolactin level in lactational rats].

AIM: To study the antagonism of l-stepholidine (SPD) against bromocriptine (Bro)-inhibition on prolactin (PRL) level. METHODS: Bro (0.5 mg.kg-1.d-1, s.c.) reduced the PRL and caused a dysplasia of mammary gland in lactational rats. The weight growing of newborn rats was retarded. The PRL of the lactational rats was assessed by immunoradiometric assay (IRMA); the weight of newborn rats and development of mammary glands in lactational rats were also examined. Antagonism of SPD was evaluated. RESULTS: SPD (30 & 100 mg.kg-1.d-1, i.p.) obviously antagonized the Bro that induced lowering the PRL level in lactational rats, the PRL was 11 +/- 4 & 23 +/- 6 micrograms.L-1 (NS 7 +/- 2) respectively on d 15 of postpartum and the development of mammary gland in lactational rats was normal. The newborn rats grew rapidly in 11-15 d. CONCLUSION: SPD possessed an antagonism with Bro inhibition on D2 receptors located in the pituitary gland, and was an antagonist of dopamine D2 receptors.

Animals↗
PubMed1996

[Blockade of (+/-) 12-chloroscoulerine on feed-back regulation of dopamine D2 autoreceptors].

AIM: To verify whether (+/-) 12-chloroscoulerine (CSL) is antagonist or agonist effect to D2 autoreceptors. METHODS: The levodopa content accumulated in the rat striatum was measured by HPLC-ECD, and the DA neuron firing activity in the substantia nigra zona compacta (SNC) was recorded. RESULTS: The accumulated levodopa content induced by CSL 40 mg.kg-1 was much more than that of 1,4-butyro-lactone (BL) group (P < 0.01). After i.p. injection of apomorphine (Apo) 5 mg.kg-1, the levodopa content was decreased below that of BL group (P < 0.05). The Apo inhibition on levodopa content was completely reversed by CSL (40 mg.kg-1, i.p.) and then increased the levodopa content (2.5 +/- 1.1 micrograms.g-1) over that of Apo group (0.7 +/- 0.3 microgram.g-1, P < 0.01). In the electrophysiologic recording, Apo (15 micrograms.kg-1, i.v.) induced the decrease of SNC DA cell firing rate nearly to zero. At the accumulated dose of CSL up to 80 micrograms.kg-1 (i.v.), the inhibition of Apo was attenuated and the firing activity was restored to predrug level. CONCLUSION: CSL showed an antagonistic action, an action to D2 autoreceptors.

Animals↗