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Biomedical subjects

D H Chen

Publications and source records attributed to D H Chen.

At least 37 records · Page 2Linked to original sources
PubMed1994

A nuclear tRNA gene cluster in the protozoan Leishmania tarentolae and differential distribution of nuclear-encoded tRNAs between the cytosol and mitochondria.

All mitochondrial tRNAs in the protozoan Leishmania are believed to be encoded in the nuclear genome and imported selectively into the mitochondria by an as yet unknown mechanism. Previously, we reported that two tRNAs whose genes are tightly linked were imported by mitochondria. In contrast, a tRNA encoded by a lone tRNA gene was not detectable in mitochondria. The lone tRNA gene had flanking sequences that were different from the linked genes. These studies implied a possible correlation between tRNA gene organization and gene flanking sequence, and selective tRNA import into mitochondria. Here, we report the identification of a cluster of 10 tRNA genes and show the distribution of the corresponding tRNAs in cytosolic and mitochondrial fractions. tRNA(leu)(CAG) and tRNA2(arg)(TCG) are abundant in the cytosol, but relatively scarce in mitochondria. Conversely, tRNA(ile)(TAT) and tRNA1(lys)(TTT) are abundant in mitochondria, but relatively scarce in the cytosol. tRNA(val)(TAC) and tRNA2(thr)(TGT) are barely detectable in either cellular compartment, while tRNA(gln)(TTG), tRNA1(arg)(ACG), tRNA(gly)(TCC), and tRNA(trp)(CCA) are detected in approximately equal levels in both compartments. Sequencing of the 2600 bp that comprise the tRNA gene cluster also encoding the genes for 5S RNA and URNAB RNA indicates that nucleotide composition, length, and location of genes within the cluster do not clearly correlate with import characteristics. The unexpected presence of the tRNA(trp)(CCA)-gene transcript in mitochondria is also reported. Evidence suggests that this tRNA may have unidentified base modifications at the anticodon triplet.

Animals↗
PubMed1994

In vivo expression and mitochondrial import of normal and mutated tRNA(thr) in Leishmania.

Evidence suggests that mitochondria of protozoans and plants contain nuclear-encoded tRNAs. In trypanosomatids, the entire set of tRNAs in the mitochondria are presumably imported from the nucleus, but the mechanism of tRNA import is not presently understood. In this study, we have employed a plasmid-encoded nuclear tRNA gene as a means of investigating tRNA expression and mitochondrial import in vivo in Leishmania tarentolae. Using a Leishmania plasmid, we cloned a 1-kb or 250-bp restriction fragment carrying the nuclear tRNA(thr) gene and three in vitro mutagenized derivatives: Tac6 (an insertion of 6 nucleotides at the anticodon loop), Td4 (a 4-nt insert at the D-loop) and Tv4 (a 4-nt insert at the variable arm). Leishmania cells stably transfected with these plasmids were then examined for tRNA expression and import by Northern analysis. The results show that the plasmid-encoded wild type tRNA(thr) gene produced a significantly elevated level of expression in the cytosol. Similarly, the Tac6-transfected cells exhibited a large abundance of the mutant RNA relative to the normal tRNA (chromosome-encoded gene transcripts) in the cytosol. Furthermore, the mutant Tac6 RNA was found imported into mitochondria, although the proportion of the mutant vs. normal tRNA in mitochondria was greatly reduced as compared to that in the cytosol. We suggest that the mitochondrial import machinery is capable of discriminating against the mutant RNA in favor of the normal tRNA for import. In another example, we found that the Tv4 gene showed expression, albeit somewhat reduced, but its import into mitochondria was completely blocked. Unexpectedly, the 4-base addition mutation (Td4) at the D-loop showed neither expression nor import. While these results clearly signify the importance of various segments within the tRNA gene for in vivo expression, our data underscore the significance of the variable loop for mitochondrial import. It is our belief that this plasmid-encoded tRNA gene expression system in Leishmania may be useful in gaining further insights on tRNA import.

Animals↗
PubMed1994

Determination of the contents of EPA and DHA and lipid constituents in main fresh water fishes in China.

In this study the molecular formula and structure of lipid constituents of silver carp and bighead carp in middle reaches of Yangtze River were determined by gas chromatography-mass spectrometry. The position of double bounds was identified by the method of double bounds chemical localization. These carps are proved to contain eicosapantaenoic acid (EPA) and decosahexenoic acid (DHA). The contents of EPA and DHA, which were determined by gas chromatography, in silver carp and bighead carp were approximately the same as in tuna and salmon. The contents of EPA and DHA in 100 g wet sample were 0.187 g, 0.229 g and 0.246 g, 0.325 g respectively, but the cholesterol contents in silver carp and bighead carp were much lower than in tuna and salmon.

Animals↗
PubMed1993

Selective import of nuclear-encoded tRNAs into mitochondria of the protozoan Leishmania tarentolae.

The trypanosomatid mitochondrial genome does not encode tRNA genes at all and experimental evidence obtained with Leishmania tarentolae shows that tRNAs in mitochondria represent a selected set of imported nuclear-encoded tRNAs. In this paper we present the data showing that tRNAs derived from the clustered genomic tRNA genes are invariably imported into mitochondria, while tRNA from the solitary gene is not. By sequencing a cosmid DNA clone of L. tarentolae genomic DNA, we have identified a 1.5-kb subclone encoding a duplicate set of the closely linked tRNA(Tyr) (GTA) and tRNA(Thr) (AGT) genes. Northern analysis shows that these tRNAs are imported into mitochondria. In contrast, when the tRNA gene [tRNA(Gln) (CUG)] located alone in a 40-kb DNA fragment was examined, the corresponding tRNA was not detected in the mitochondrion. This "loner" tRNA gene is highly unusual since the 3'-flanking putative RNA polymerase III transcription termination signal sequence is characterized by a long string of 8 Ts followed by an A and a stretch of 7 Cs, while all other trypanosomatid tRNA genes whose tRNA transcripts are imported are terminated by a possible transcription termination signal of only 4-6 Ts. Whether the correlation found between the gene organization and tRNA-import characteristics is of general significance needs to be investigated further. A simple computer analysis presented in this paper rules out the possibility that tRNAs found in the trypanosomatid mitochondrion are the products of the U-addition type 'RNA editing' of maxicircle DNA.

Animals↗
PubMed1992

A study on the removal of urea from aqueous solution with immobilized urease and electrodialysis.

A five-compartment electrodialyzer with immobilized urease was developed for the removal of urea from aqueous solution. The immobilized urease, supported on polyurethane foam, was placed in the central (dilute) compartment, where urea was hydrolyzed and the products NH4+ and CO3(2-)/HCO3- were removed simultaneously by electrodialysis. The system was studied both under constant current and under constant voltage. The effects of urea concentration and applied current or voltage on the removal of urea and ammonium ions from the dilute solution were investigated. The variations of the pH of dilute solution, the current or voltage of system, and current efficiency were also examined during reaction-electrodialysis. The removal of urea by enzymic reaction was not affected significantly by the applied electric field. The current efficiencies for removing ammonium ions from dilute solution were mostly within 40-80%, and the removal percentage of ammonium ions was dependent on current density and current efficiency.

Dialysis↗
PubMed1992

Cigarette smoking among junior high school students in Beijing, China, 1988.

Prevalence, behavioural patterns and risk factors of cigarette smoking were studied in a sample of 8437 junior high school students in Beijing in 1988. Smoking at least occasionally was reported by 34.4% of boys and 3.9% of girls, though the intensity tended to be low. Smoking prevalence increased with age among boys. Inhaling smoke into the lungs was practised by 68.2% of the boys who smoked and 37.3% of the girls. 'Believing that one looks elegant when smoking', 'trying to be fashionable' and 'seeking stimulation' were the most important reasons for smoking. Of the boys 83.5% and of the girls 86.5% usually smoked with friends or schoolmates. Many more boys (19.2%) than girls (1.7%) smoked at home. Examinations of risk factors for teenage smoking showed that it was associated with a combination of familial, psychological and socio-school factors, with peer group pressure being the most important one.

Adolescent↗
PubMed1992

1-Phenyl-3-trimethylaminopropyl carbodiimide: a new inhibitor of thymidylate synthase.

Thymidylate synthase (EC 2.1.1.45) from methotrexate-resistant Lactobacillus casei was inactivated by 1-phenyl-3-trimethylaminopropyl carbodiimide (PTC), 1-phenyl-3-dimethyl aminopropyl carbodiimide (PDC), and 1-ethyl-3-dimethyl aminopropyl carbodiimide (EDC). In the presence of excess PTC, the inactivation followed pseudo-first order kinetics; the second order rate constant was approximately 200 M-1min-1 at 30 degrees C. The rate of inactivation by PTC was faster than that by either PDC or EDC. Concentrations of the substrate dUMP greater than 0.15 mM, or of the product dTMP greater than 1.6 mM completely protected the enzyme from inactivation by PTC, but 10 mM dUrd provided very little protection. The rate of inactivation of EDC was reduced by only 40% in the presence of 50 mM dUMP. Nucleophiles (sulfanilic acid, glycine methyl ester, or glycine ethyl ester) had no effect on the rate of inactivation by PTC. The complete inactivation of thymidylate synthase by PTC was accompanied by the incorporation of approximately 2 mols of 14C-PTC per mol of enzyme. Although carbodiimides normally modify carboxyl groups in proteins, results from sulfhydryl group titrations and from reversible modification of sulfhydryl groups by methyl methanethiosulfonate suggest that two of the four cysteine residues of thymidylate synthase were modified by PTC.

Carbodiimides↗
PubMed1991

[Treatment of climacteric syndrome with new gengnian prescriptions].

It was found by the observations of clinical treatment that the three indexes of epinephrine(E), norepinephrine(NE) and dopamine(D) of urinary catecholamine(CA) increased (P less than 0.001, P less than 0.05 and P less than 0.001) for the climacteric patients who suffered from the deficiency of Yin leading to the hyperactivity of the internal heat of the heart, and the urinary 17-hydroxycorticosteroid (17-OHCS) increased (P less than 0.001) for the patients who suffered from the deficiency of Yin leading to the hyperactivity of the internal heat of the liver. Both the three indexes and urinary 17-OHCS increased for the two groups (P less than 0.01). However, for all the above groups who suffered from the deficiency of Yin leading to the hyperactivity of the internal heat, the NE/E ratio was larger than the normal ratio, which stands for the level of central catecholamine. After the treatment with new Gengnian prescriptions, the clinical symptoms of the patients were improved, and in the meantime urinary CA. 17-OHCS and NE/E were decreased. The total efficiency was 89.2%. The principle of treatment with this prescription may be due to the fact that the level of central catecholamine decreased so that the excessive excitation of sympathetics-adrenocortical system and sympathetics-adrenocortical system was restrained.

17-Hydroxycorticosteroids↗
PubMed1991

[Ultrastructural study of the lethal effect of lymphokine activated killer (LAK) cell on liver cancer cells].

Co-cultured subcloned LAK cell and human liver cancer cell (H7402) were fixed in situ for scanning electron microscopic and transmission electron microscopic examinations. The SEM and TEM findings gave a new evidence in answering how LAK cells kill the cancer cells. First, the activated killer cells recognized and made close contact with the target cell. Then some kind of lethal hit produced by intact killer cells was delivered, injuring the target cell, boring holes and pole-like tunnels on the cell surface or even penetrating into the cytoplasm of the cancer cells. Eventually, cell death in the manner of apoptosis and necrosis occurred as the end result of the damage to the cancer cell. These findings strongly support the idea that the death of the target cells is mediated by LAK cells.

Humans↗
PubMed1990

[Study of characteristics of monoclonal antibody against substance P].

Cross-reaction of a rat monoclonal antibody (BTP-1) against seventeen substance P analogues was studied. The antibody was of IgG type and related to the carboxyl terminal of substance P, especially methionyl in the terminal, but did not depend on the strength of antagonistic effects of these analogues. It did not show cross-reaction with the following nine peptides: glucagon, endorphin, angiotensin I, II, leucine-enkephalin, methionine-enkephalin, bradykinin, oxytocin and dernorthin, indicating its high specificity to substance P. By means of immuno-enzyme histochemical method, it was shown that stained nerve fibers were located in the gelaliternous substance of Rolando, interpeduncular nucleus, substantia nigra and nerve cell bodies in the vestibular nucleus, lateral tegmental nucleus of mesencephalon and ventral region of third ventricle.

Animals↗
PubMed1989

[An electron microscopic study of viral infected peripheral mononuclear cells in epidemic hemorrhagic fever].

Ultrathin sections of peripheral blood cells from 7 patients of early stage epidemic hemorrhagic fever (EHF) were reexamined under transmission electron microscope. Virus particles were found in the cytoplasmic vacuoles of mononuclear cells from two patients. The morphology and morphogenesis of the matured virus were identical with those of Hantaan virus of the Bunyaviridae family. Additionally, abnormal aggregations of tubuloreticular structure (TRS) were sometimes encountered in the dilated cisternae of endoplasmic reticulum in the lymphoid cells regardless of whether there are virus particles present in the cytoplasm.

Orthohantavirus↗