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Biomedical subjects

S T Chung

Publications and source records attributed to S T Chung.

16 recordsLinked to original sources
PubMed1992

Effects of methylguanidine on sodium and organic ion transport.

We studied the acute effect of methylguanidine (MG), a suspected uremic toxin that accumulates in renal failure, on p-aminohippurate (PAH) and tetraethylammonium (TEA) uptake in rabbit kidney slices, on Na+,K+ ATPase activity in the microsomal fraction of rabbit kidneys, and on transepithelial active Na transport across toad skin. MG at concentrations ranging from 0.05 (similar to that reported in uremic patients) to 1.0 mM does not affect the organic anion (PAH) uptake, although it exhibits a concentration-dependent inhibition of organic cation (TEA) uptake. MG at concentrations from 0.05 to 5 mM had no effect on kidney Na+,K+ ATPase activity or on active transepithelial Na transport across toad skins when applied to the outside bathing solution; however, MG (greater than 1 mM) stimulated Na transport when applied to the inside bathing solution. These results are not consistent with the hypothesis that MG is a potential uremic toxin that causes the natriuresis and other toxic effects. However, long-term toxic effects of MG on the kidney were not assessed in the present study.

Analysis of Variance↗
PubMed1992

Isolation and identification of 3-propylidene-delta 1-pyrroline-5-carboxylic acid, a biosynthetic precursor of lincomycin.

An accumulated lincomycin intermediate in UC 8292, a lincomycin nonproducing strain of Streptomyces lincolnensis, has been isolated and purified by employing an assay system based on complementation of UC 11066, another lincomycin nonproducing strain of S. lincolnensis. The structure of the purified intermediate is shown to be 3-propylidene-delta 1-pyrroline-5-carboxylic acid, or 1, 2, 3, 6-tetradehydro-propylproline by mass spectrometry and NMR spectroscopic studies. Based on the structure of this newly found intermediate, a biosynthetic pathway for propylproline is proposed as tyrosine-->L-3-hydroxytyrosine (Dopa)-->-->-->-->3-propylidene-delta 1-pyrroline-5-carboxylic acid-->3-propyl-delta 2-pyrroline-5-carboxylic acid-->propylproline.

Fermentation↗
PubMed1991

Length-tension recording system for strabismus surgery.

To meet the need for both scientific information and a clinical means for measurement of the mechanical parameters of the most difficult individual strabismus cases we present a technique for directly measuring and plotting the length-tension characteristics of the tissues supporting the eye. Semiconductor strain gauges mounted on the shanks of a custom machined eye forceps and an ultrasonic method of making continuous duction measurements of the eye have proved feasible. When the forceps are interfaced with a dedicated microcomputer, the system provides a permanent, quantitative, length-tension record displayed in real-time. The instrumented length-tension forceps system has provided a noninvasive means for quickly and simply assessing the mechanical underlying determinants of strabismus pathology in the office, the laboratory or in the operating room, and can aid in the planning and immediate intraoperative alteration of strabismus surgery. Under operator coordination, measurements can be made which precisely define the mechanical load which the eye muscles must move. The resulting objectively determined tissue stiffness asymmetries and muscle restrictions limiting ocular motion indicate the purely mechanical contributions to a patient's strabismus. Measurements of active force indicate the magnitudes and patterns of innervation over the entire range of gaze. By comparison of these active force and passive stiffness records, nerve signal imbalances may be quantitatively distinguished from mechanical imbalances in strabismus. It is the detailed interaction of these nonlinear muscle forces and mechanical elements which determines the position of each eye in strabismus and therefore the proper surgical treatment. A brief description of actual use and a few examples of clinical results are included from over 200 human records.

Calibration↗
PubMed1990

Nucleotide sequence of Streptomyces fradiae transposable element Tn4556: a class-II transposon related to Tn3.

The first transposable element to be isolated from Streptomyces fradiae, Tn4556, was completely sequenced; the total of 6625 bp have an overall G + C composition of 68%. Computer-aided analysis of this sequence reveals the location of nine open reading frames (ORFs). Several of these ORFs, numbers 1, 2, and 7, contain ribosome-binding sites (RBS) near their putative translation-initiation sites, which share identity with the consensus RBS sequences of Escherichia coli and Bacillus subtilis. ORF1 potentially encodes an 892-amino acid (aa) protein and this deduced aa sequence shares 61% identity with that of the transposase encoded by the tnpA gene of Tn3. Three other ORFs, 2, 3 and 5, potentially encode proteins which are similar in size to the resolvase protein encoded by the Tn3 gene tnpR; however, none of the protein products deduced from these ORF share extensive aa sequence identity with other resolvase proteins.

Amino Acid Sequence↗
PubMed1987

Tn4556, a 6.8-kilobase-pair transposable element of Streptomyces fradiae.

A 6.8-kilobase-pair (kbp) transposable element (Tn4556) was found in a neomycin-producing strain of Streptomyces fradiae. This element was first observed in two 30.3-kbp plasmids (pUC1123 and pUC1124) which arose when a thiostrepton resistance gene (1 kbp) was ligated with the BclI-2 fragment (22.5 kbp) that contains the origin of replication of phage SF1. The Tn4556 segment was deleted when these plasmids were transduced into another S. fradiae host with phage SF1. These deletion plasmids (pUC1210 and pUC1211) had copy numbers of less than 1 per chromosome and were unstable. In contrast, pUC1123 and pUC1124, with copy numbers of 12 to 15 per chromosome, respectively, were relatively stable. When pUC1210 and pUC1211 were reintroduced into S. fradiae by protoplast transformation, the Tn4556 element transposed again to the plasmids at numerous new locations in either of two orientations. A copy of Tn4556 was found in the S. fradiae chromosome by hybridization studies. It appears that Tn4556 originated from the chromosome, transposed into unstable pUC1210 and pUC1211, and made stable plasmids. A temperature-sensitive hybrid plasmid carrying a viomycin resistance derivative of Tn4556 (pMT660::Tn4556::vph) was constructed. When Streptomyces lividans UC8390 containing the hybrid plasmid was grown at 39 degrees C, Tn4556::vph (Tn4560) transposed to random positions in the host chromosome.

Cloning, Molecular↗
PubMed1983

[Antibiotic susceptibility of Pseudomonas aeruginosa].

The susceptibility of 128 clinical isolates of Pseudomonas aeruginosa against amikacin, kanamycin, gentamycin, minocycline, colistin, chloramphenicol, claforan , piperacillin and carbenicillin were tested. Piperacillin, carbenicillin, amikacin and claforan are effective against at least 54% of strains tested. The susceptibilities of microorganisms to antibiotics were evaluated in different points and discussed in details.

Anti-Bacterial Agents↗
PubMed1982

Isolation and characterization of Streptomyces fradiae plasmids which are prophage of the actinophage phiSF1.

Two plasmids, designated pUC1 and pUC13, have identified as different prophage states of the Streptomyces fradiae actinophage phiSF1. Plasmids pUC1 and pUC13, 51.1 Md, are identical as determined by restriction endonuclease analysis and other criteria. They differ in that while pUC1 specifies "type A" plaques, characterized by a narrow zone of growth inhibition around a transformant colony, pUC13 specifies "type B" plaques, characterized by concentric rings of growth and growth inhibition around a transformant colony. Additionally cultures carrying pUC13 release antinophage phiSF1 at a frequency about 10 3-10 4 times that pUC1 containing cultures. Restriction enzyme digestion, transfection, and transformation analyses show that phiSF1 DNA, 55.7 Md, is about 8-10% larger than pUC13 and appears to be circularly permuted and terminally redundant. The pUC1 and pUC13 prophage are interconvertible.

Bacteriophages↗
PubMed1982

Metabolic accumulation of hydrocarbons by Acinetobacter species.

Acinetobacter HO1-N grown on hexadecane as a sole source of carbon and energy was demonstrated to cytoplasmically sequester this hydrocarbon. Cultures grown with hexadecane and heptadecane accumulated intracytoplasmically both hydrocarbons. The accumulation of specific alkanes was non-specific while the oxidation of the pooled hydrocarbon was highly specific. Naphthalene was highly inhibitory to the growth of this microorganism but slowly co-oxidized in the presence of hexadecane.

Acetates↗
PubMed1974

Apparent mutagenic effect of induction of lambda prophage inserted between lysA and thyA.

Induction of a heat-inducible abnormal lambda prophage inserted between lysA and thyA in Escherichia coli resulted in a number of auxotrophic mutants in the surviving cured-cell populations. These mutants could not be accounted for by deletions arising on formation of lambda hybrid particles carrying regions adjacent to the insertion site. The properties of these mutants, which were almost all spontaneously revertable, have been described and mapped by F' episome complementation. Tentatively, it was suggested that induction of the lambda lysogen leads to a mutagenic state.

Arginine↗
PubMed1973

Loss of an essential function of Escherichia coli by deletions in the thyA region.

In an attempt to obtain deletions in the thyA gene, an abnormal lysogen of lambda having the prophage inserted between the thyA and lysA genes was induced, and the surviving cured cells were examined for Thy(-) and Lys(-) mutants. In nearly 10,000 cured cells, 184 Lys(-) but no Thy(-) mutants were found. At the same time, the induced lambda phage contained an approximately equivalent number of lambdathyA(+) and lambdalysA(+) transducing particles. By contrast, in a strain with the genotype F' thyA(-)lysA(+)/ thyA(+)lysA(+), induction of the abnormal lambda lysogen gave rise to many Thy(-) mutants in the cells cured of the prophage. In these Thy(-) mutants it was not possible to eliminate the episome with acridine orange, although the episome could be removed in control cultures with a thyA(+) allele in the resident gene. Therefore, it was suggested that deletion of a gene in the region of the chromosome from the position of the insertion of the lambda prophage through the thyA gene caused loss of an essential and diffusible function.

Acridines↗