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Biomedical subjects

T C Chen

Publications and source records attributed to T C Chen.

At least 253 records · Page 14Linked to original sources
PubMed1980

Guanosine triphosphate: an endogenous compound in the rabbit cerebellar cortex which couples the beta-adrenergic receptor to adenylate cyclase.

The guanyl nucleotides GTP and GDP are endogenous factors in the rabbit cerebellum which contribute to the in vitro coupling of the beta-adrenergic receptor to adenylate cyclase. Repeated washing of the particulate material removes these endoactivity to beta-adrenergic agonists. The endogenous GTP and GDP, isolated by high pressure liquid chromatography, mimic the ability of the supernatant both to restore the coupling of receptor and enzyme and to increase basal enzyme activity. The effectiveness of GDP reflects its conversion to GTP during the assay. GTP does not affect either the number of [3H]dihydroalprenolol binding sites or the affinity of these sites for L-isoproterenol; furthermore, GTP does not cause a shift in activation affinity of enzyme activity for isoproterenol. Thus, the guanyl nucleotides are endogenous constituents of the mammalian brain which are essential for the functional 'coupling' of beta-adrenergic receptors to adenylate cyclase.

Adenylyl Cyclases↗
PubMed1980

Endogenous components of the striatum confer dopamine-sensitivity upon adenylate cyclase activity: the role of endogenous guanyl nucleotides.

Repeated washing of the particulate material from rat striatum abolishes the dopamine-sensitivity of the adenylate cyclase activity. Readdition of the soluble fraction of the caudate homogenate restores the dopamine-sensitivity to the enzyme activity. Fractions, prepared with thin layer chromatography, containing endogenous GTP and GDP also restore dopamine-sensitivity to striatal adenylate cyclase activity. The effectiveness of GDP results from its conversion to GTP during the assay; when this conversion is eliminated, GDP can specifically block the coupling between the dopamine receptor and adenylate cyclase.

Adenylyl Cyclases↗
PubMed1979

Apolipoprotein A-II: chemical synthesis and biophysical properties of three peptides corresponding to fragments in the amino-terminal half.

Three peptide fragments of apolipoprotein A-II corresponding to residues 17--31, 12--31, and 7--31 have been synthesized by solid-phase techniques and purified to apparent homogeneity. Each of these fragments contains residues 18--30, a region previously proposed to possess potential amphipathic helical properties. Secondary structural changes of these synthetic fragments accompanying their interaction with phospholipid have been studied by circular dichroism. The magnitude of this interaction has been evaluated from the yields and stoichiometry of lipid-protein complexes isolated by density gradient ultracentrifugation. Fragment 17--31, the smallest peptide containing the proposed amphipathic helix, did not interact with dimyristoylphosphatidylcholine (DMPC) single bilayer vesicles at 24 degrees C; upon addition of DMPC, no ellipticity change could be detected nor could a stable lipid-peptide complex be isolated. However, fragments 12--31 and 7--31 did interact with phosphilipid; in the absence of lipid, both fragments had primarily disordered structures, but when isolated as DMPC-peptide complexes, both fragments possessed increased helical structure. The phospholipid:peptide molar ratio was 14:1 for fragment 12--31 and 27:1 for fragment 7--31. Studies of space-filling models of these fragments suggest that hydrophobicity and/or length are important properties of phospholipid binding apoproteins.

Amino Acid Sequence↗
PubMed1978

Replication of bacteriophage M13. XIV. Differential inhibition of the replication of M13 and M13 miniphage in a mutant of Escherichia coli defective in the 5' leads to 3' exonuclease associated with DNA polymerase I.

Previous studies have shown that M13 single-strand synthesis is inhibited at nonpermissive temperature in Escherichia coli polAexl, a temperature-sensitive mutant defective in the 5' leads to 3' exonuclease activity of polymerase I (T.-C. Chen and D. S. Ray, J. Mol. Biol. 106:589-604, 1976). Under these conditions the formation of covalently closed replicative form (RF) molecules is greatly reduced, and miniature forms of RF accumulate. We show here that the accumulation of mini-RFs is the consequence of a differential inhibition of the replication of unit-length phage and preexisting miniphage rather than a de novo production of miniphage. Mini-RFs do not accumulate even after as many as nine cycles of growth in the mutant host infected only with unit-length phage. Mixed infections of the mutant host with plaque-purified unit-length phage and a single cloned miniphage show that discontinuities in the mini-RFs are joined with higher efficiency than are those contained in unit-length RFs. After a shift to nonpermissive temperature during single-strand synthesis in cells infected with plaque-purified phage alone, M13 RFs are found largely as RFII molecules (RF form having one or more single-strand discontinuities) containing only a single discontinuity in the viral strand. The inability of the accumulated unit-length RFII molecules to actively replicate may reflect the presence of either a bound protein or RNA primer on the 5' terminus of the viral strand and provides further support for the existence of distinct initiation and termination events in the synthesis of the viral strand.

Coliphages↗
PubMed1976

Microbiological quality of frozen fried chicekn product obtained from a retail store.

Two brands of frozen fried chicken products were purchased monthly from a local supermarket for six months. Microbiological qualities of these samples were studied. The log number of mesophilic counts ranged from 2.90/g. to 4.78/g; log psychrophilic counts varied from 2.74/g. to 4.66/g.; and log Staphylococcus- 110 medium counts ranged from 2.84/g. to 4.54/g. Mean log microbial counts were higher in brand A samples than in brand B samples. No yeast or mold was detected and all samples were Salmonella negative. Most samples were negative in coliform test, except five samples had coliform MPN ranging from 0.5/g to 0.8/g. A total of 144 isolates of psychrophiles from 12 samples was tentatively identified to be members of Staphylococcus species. About 82.2% of the isolates belong to the Subgroup VI Staphylococcus according to Baird-Parker's classification. Another 17.8% of the isolates resembled Subgroup vi Staphylococcus except in phosphatase test.

Animals↗
PubMed1976

Studies on shigella isolated in southern Taiwan.

During 1969, a total of 1,476 fecal and rectal swab specimens was collected from children with diarrhea and 249 strains of shigella were isolated. The incidence was 16.9%. The serotypes of 249 strains were: Shigella dysenteriae, 1.6% (4 strains); S. flexneri, 73.1% (182 strains); S. boydii, 3.2 (8 strains) and S. sonnei, 22.1% (55 strains). There was no marked difference of the isolation rate throughout the whole year. The susceptibility of shigella isolates to chemotherapeutic agents were also investigated. The percentage of the strains susceptible to gentamicin was 97.2%; to cephaloridine, 93.2%; to kanamycin, 91.9%; to colistin, 91.6%; to hetacillin, 88.4%; to ampicillin, 82.4% and to nalidixic acid, 79.9%. The other tested chemotherapeutic agents were less effective.

Anti-Bacterial Agents↗
PubMed1974

Taxonomic significance of phenethyl alcohol production by Achromobacter isolates from fishery sources.

The formation of phenethyl alcohol from L-phenylalanine and ethanol by achromobacter isolates of fishery origin was found to be taxonomically significant for such organisms. Phenylpyruvate, the direct oxidative deamination product of L-phenylalanine, was found to serve as an intermediate precursor to phenethyl alcohol formation. Among ten Acinetobacter isolates examined, none produced phenethyl alcohol. Among nine Moraxella isolates examined, one produced phenethyl alcohol.

Acinetobacter↗