Biomedical subjects

J M Li

Publications and source records attributed to J M Li.

At least 109 records · Page 6Linked to original sources

PubMed1990

Effect of cyclosporin A on the ontogeny of different T cell sublineages in chickens.

We have used a panel of murine mAb against chicken TCR and associated molecules to study the effect of cyclosporin A (CsA) on the ontogeny of the different sublineages of T cells. After injection of CsA (20 mg/kg/day from day 0 to 20) we observed a significant suppression of the normal maturation of the TCR2 (alpha beta TCR) cells in their transition from cortical CD4+CD8+ thymocytes to the mature single positive cells in the thymus medulla. The TCR3 subpopulation, a distinct form of alpha beta-like TCR in chickens, was inhibited from initially developing within the cortex by CsA, indicating that the TCR3 subpopulation is functionally distinct from the TCR2+ cells. In contrast, the maturation and peripheral emigration of TCR1 (gamma delta TCR) cells was unaffected by CsA treatment. Mature splenic T cells sorted for either TCR1+ or TCR2+ subsets were equally sensitive to CsA blockade of Con A-stimulated mitogenesis, indicating that there is no inherent difference in CsA sensitivity between these sublineages. Furthermore, no difference was detected in the expression of class II MHC Ag in thymi of birds treated with olive oil vs CsA. Inasmuch as the mechanism of CsA action appears to involve inhibition of TCR initiated signal transduction for lymphokine synthesis, these data indicate that a similar signaling is involved in thymic repertoire selection for TCR2. The lack of an effect on TCR1 cell maturation suggests that the TCR1 repertoire may not undergo selection in the thymus as do TCR2+ cells.

Animals↗

PubMed1990

Translocation mechanism of Na-Ca exchange in single cardiac cells of guinea pig.

We have studied in single cardiac ventricular cells of guinea pig the ionic translocation mechanism of the electrogenic Na-Ca exchange, i.e., whether Na and Ca ions countercross the membrane simultaneously or consecutively with "ping pong" kinetics. The dose-response relation between the external Ca concentrations [( Ca]o) and the current density of the outward Na-Ca exchange current were measured at three different intracellular Na concentrations [( Na]i) in the absence of external Na. Nonlinear regression curves of the dose-response relation obtained by computer revealed Michaelis-Menten type hyperbola from which the [Ca]o giving a half-maximal response (apparent KmCao or K'mCao) and the apparent maximum current magnitude (I'max) were estimated at each [Na]i. As [Na]i increased, the K'mCao increased progressively and the value of K'mCao/I'max tended to decrease. These results are consistent with the simultaneous mechanism. The K'mCao/I'max values, however, were small and close to each other, so it was not possible to completely preclude a consecutive mechanism.

Animals↗

PubMed1990

[Modulation of norepinephrine release in sympathetic nerve endings in renal hypertensive dogs].

Experimental renal hypertensive and normal dogs with femoral arteries constantly perfused were studied. Cocaine was used to block the presynaptic norepinephrine (NE) reuptake and tyramine to initiate the release of NE in sympathetic nerve endings. NE spillover and infusion pressure were measured under basic conditions and during intraarterial infusion of cocaine, tyramine and in combination with alpha 1 and alpha 2 adrenoceptor antagonists. The extent of NE spillover increase induced by infusion of tyramine, the increased infusion pressure by cocaine and tyramine, and the reduced infusion pressure by prazosin were all greater in hypertensive dogs than those in normal dogs, but adrenoceptor antagonist idazoxan further increased tyramine-induced NE spillover in normal dogs only. It was suggested that reduced-regulation of presynaptic alpha 2 adrenoceptors to NE release and increased responsiveness of postsynaptic alpha 1 adrenoceptors to NE were present in hypertensive dogs.

Adrenergic alpha-Antagonists↗

PubMed1989

Cloning and structure of the hem A gene of Escherichia coli K-12.

An Escherichia coli gene, which complements two independent hemA mutants of E. coli, has been cloned onto a multi-copy plasmid and both its strands have been sequenced. Both complemented mutants produce 5-aminolevulinic acid (ALA) and display fluorescence after 24h. The cloned sequence appears to encode a 46-kDa protein, which when produced in the maxicell procedure is processed to a 41-kDa protein as determined by sodium dodecyl sulfate-polyacrylamide-gel electrophoresis. The amino acid sequence of the cloned gene product shows no significant homologies with any cloned ALA synthase, nor with any protein, in two E. coli databanks. A second cloned gene fragment, which has its coding region 34 bp away from the coding region of the gene that complements hemA, has been identified as part of protein release factor 1(RF1), thus confirming the location of hemA at min 26.7 and mapping it precisely near RF1. We have shown that E. coli utilizes the intact five-carbon chain of glutamate for the synthesis of ALA [Li et al., J Bacteriol. 171 (1989b) 2547-2552].

Aldehyde Oxidoreductases↗

PubMed1989

The structure of the Escherichia coli hemB gene.

The Escherichia coli hemB gene, which encodes 5-aminolevulinic acid dehydratase, and was cloned into pTZ18U, a multicopy plasmid, was sequenced. The hemB insert was double-digested with restriction enzymes and recloned back into pTZ18U and pTZ19U to allow for sequencing in two directions. In a second procedure, used to fill in gaps and to confirm the sequence derived from the first procedure, the whole insert was cloned into M13 phages. A nested set of deletions was constructed and recloned into M13. Both the double-digested fragments cloned into plasmids pTZ18U and pTZ19U and the overlapping fragments contained in M13 phages were sequenced using the dideoxy procedure with [35S]dATP. Computer software was used to identify coding regions and the correct reading frame. Two promoter regions, two Shine-Dalgarno sequences and two possible start sites were identified. Extensive homologies with yeast (36%), human liver (40%) and rat liver (40%) amino-acid (aa) sequences were observed, especially in the 16-aa Zn-binding region (75%) and the 4 aa surrounding the essential lysine at the active site (100% for rat and human proteins). Computer analysis of promoter strength and two independent analyses of codon usage indicated that the hemB gene is moderately expressed.

Amino Acid Sequence↗

PubMed1989

Slow transport of freely movable cytoskeletal components shown by beading partition of nerve fibers in the cat.

To account for the transport in nerve fibers of tubulin and neurofilament proteins in slow component a, the Structural Hypothesis holds that these proteins are assembled into microtubules and neurofilaments in the cell bodies and the cytoskeletal organelles then moved down in the fibers as part of an interconnected matrix at a uniform rate of about 1 mm/day. The Unitary Hypothesis, on the other hand, considers these proteins to be carried down within the fibers as soluble components or as freely movable small polymers or subunits turning over locally in the stationary cytoskeleton. To differentiate between the two hypotheses, cat L7 dorsal roots were taken at times from 7 to 25 days after their L7 dorsal root ganglia were injected with [3H]leucine to assess the labeling of the cytoskeleton by the use of beading and autoradiography. Beading was induced by a mild stretch and after fast-freezing and freeze-substitution of the roots for histological preparation, the beads were seen in the fibers as a series of expanded regions alternating with constrictions. In the constrictions the cytoskeleton was compacted into an area as small as 5% that of the normal axon, with the axoplasmic fluid and displaceable (freely movable) components squeezed from the constrictions into the adjoining expansions. Roots taken after 7 and 14 days, times consistent with slow component a downflow, were assessed with sodium dodecyl sulfate-polyacrylamide gel electrophoresis and their content of tubulin and neurofilament proteins shown to constitute 40-50% of all the labeled proteins present. In autoradiographs of dorsal roots taken at those times, numerous grains due to radioactivity were located over the non-constricted regions of the fibers. Few or no grains were present over the constrictions after 7 days. The findings are in accord with the labeled tubulins and neurofilament proteins being present in soluble form in the fibers and expressed from the constrictions into the expansions of the beaded fibers. In contrast, a number of fibers in roots taken at 14-20 days after injection showed somewhat higher grain densities over the constrictions, and more so after 25 days, indicating uptake of labeled subunits into the cytoskeletal organelles at later times. The results are consistent with the downflow of tubulin and neurofilament proteins as soluble components which drop off in the axon to turn over locally in their respective cytoskeletal organelles.

Animals↗

PubMed1989

N2,N2-dimethylguanosine-specific tRNA methyltransferase contains both nuclear and mitochondrial targeting signals in Saccharomyces cerevisiae.

The TRM1 gene of Saccharomyces cerevisiae encodes a tRNA modification enzyme, N2,N2-dimethylguanosine-specific tRNA methyltransferase, which modifies both mitochondrial and cytoplasmic tRNAs. The enzyme is targeted to mitochondria for the modification of mitochondrial tRNAs. Cellular fractionation and indirect immunofluorescence studies reported here demonstrate that this enzyme is also localized to the nucleus. Further, immunofluorescence experiments using strains that overproduce the enzyme show a staining at the periphery of the nucleus suggesting that the enzyme is found in a subnuclear destination near or at the nuclear membrane. There is no obvious cytoplasmic staining in these overproducing strains. Fusion protein technology was used to begin to localize sequences involved in the nuclear targeting of this enzyme. Indirect immunofluorescence studies indicate that sequences between the first 70 and 213 NH2-terminal amino acids of the methyltransferase are sufficient to target Escherichia coli beta-galactosidase to nuclei.

Amino Acid Sequence↗

PubMed1989

5-Aminolevulinic acid synthesis in Escherichia coli.

A hemA mutant of Escherichia coli containing a multicopy plasmid which complemented the mutation excreted 5-aminolevulinic acid (ALA) into the medium. [1-14C]glutamate was substantially incorporated into ALA by this strain, whereas [2-14C]glycine was not. Periodate degradation of labeled ALA showed that C-5 of ALA was derived from C-1 of glutamate. The synthesis of ALA by two sonicate fractions which had been processed by gel filtration and dialysis, respectively, was dependent on glutamate, ATP, NADPH, tRNA(Glu), and pyridoxal phosphate. tRNA(Glu) stimulated ALA synthesis in a concentration-dependent manner. Pretreatment with RNase reduced this stimulation. The amino acid sequence of the cloned insert, derived from the nucleotide sequence (J.-M. Li, C. S. Russell, and S. D. Cosloy, J. Cell Biol. 107:617a, 1988), showed no homology with any ALA synthase sequenced to date. These results suggest that E. coli synthesizes ALA by the C5 pathway from the intact five-carbon chain of glutamate.

Adenosine Triphosphate↗

PubMed1989

Effect of motherwort on blood hyperviscosity.

The effect of motherwort (Leorunus Heterophyllus Sweet, MW) on blood hyperviscosity was investigated in 105 patients. The experimental and clinical study indicated that MW has a favorable clinical impact and an effective improvement of hemorheology. MW 10 ml (5g/ml) in 250 ml of 5% glucose was given intravenously daily for 15 days. 94.5% of cases showed improvements in the form of a decrease in blood viscosity and in fibrinogen volume and an increase in the deformability of Rbc, a shorting of the time of Rbc electrophoresis and an increase in antiplatelet aggregation.

Adult↗

PubMed1989

[Some problems concerning the radiologic diagnosis of eosinophilic granuloma of the bone].

125 eosinophilic granulomas of the bone in 61 cases were reported. The radiologic manifestations may be summarized as follows: (1) Multiple lesions may occur with vertebra plana; (2) Epiphyseal lesion may be primary or secondarily involved by extension from metaphyseal lesion; (3) Metaphyseal lesion usually presents as an eccentric cystic area or central oval area of lucency; (4) The diaphyseal lesion manifests a "hole within hole" appearance; (5) The tarsal bone may exhibit a "bone within bone" sign; (6) Periosteal Codman triangle may be present.

Bone Diseases↗

PubMed1989

[Experimental observations on acrylic bone cement containing antitumor drugs].

By methods of human osteosarcoma cell culture in vitro, 3H-TdR isotope incorporation, gas chromatography and animal test, experimental observations were made on acrylic bone cement containing antitumor drugs. The results were as follows: 1. BLMA5, DACT, Ara-c, CDDP, and ADM were more thermostable. It is possible that these drugs can endure the polymerizing heat of bone cement. 2. The effective release of BLMA5, Ara-c and DACT from bone cement persisted over 2 months. 3. Scanning electron microscopy revealed that drug particles in the bone cement decreased or disappeared after immersion of the cement in tissue culture medium or implantation of it in animal bones. This shows that drug particles can be released from bone cement in vitro or in vivo 4. Animal experimental demonstrated that the bone cement containing BLMA5 or Ara-c had no effect on the healing of soft tissue, and the injury in local bone and bone marrow adjacent to the bone cement was slight and could recover in 4-8 weeks. 5. The release of residual monomer from polymerized bone cement continued as long as one month. Although the residual monomer inhibited the growth of tumor cells slightly during the early stage, it was far from being as effective as medicated bone cement.

Animals↗

PubMed1989

[Effect of berberine on slow inward ionic current in guinea pig ventricular papillary muscle].

Using a single sucrose gap voltage clamp technique, it was found that berberine hydrochloride (Ber-HCl) had a dose-dependent biphasic effect on Isi of guinea pig papillary muscle. It was more difficult to wash out the inhibitory effect of Ber-HCl on Isi. In the initial stage of the experiment, Ber-HCl 72 mumol/L and 365 mumol/L greatly improved the influx of extracellular Ca2+ and increased the amplitude of Isi. As the drug perfusion was prolonged, however, Ber-HCl dramatically blocked Ca2+ channels and decreased the influx of extracellular Ca2+ consequently, Isi was reduced in amplitude and later disappeared. This experiment further revealed the mechanisms of action of Ber on cardiac contractility and for the treatment of arrhythmias.

Animals↗

PubMed1988

Cloning of the Escherichia coli K-12 hemB gene.

An Escherichia coli heme-requiring, heme-permeable mutant had no detectable 5-aminolevulinate dehydratase or porphobilinogen deaminase activities. The gene which complemented this mutation was cloned to a high-copy-number plasmid, and porphobilinogen deaminase activity was restored to normal levels, but the synthesis of 5-aminolevulinate dehydratase increased 20- to 30-fold. A maxicell procedure confirmed that the gene cloned was hemB.

Alleles↗

PubMed1988

Evidence that the fadB gene of the fadAB operon of Escherichia coli encodes 3-hydroxyacyl-coenzyme A (CoA) epimerase, delta 3-cis-delta 2-trans-enoyl-CoA isomerase, and enoyl-CoA hydratase in addition to 3-hydroxyacyl-CoA dehydrogenase.

Genetic complementation of a mutant defective in fatty acid oxidation (fadAB) with plasmids containing DNA inserts from the fadAB region of the Escherichia coli genome was studied. The mutant containing the hybrid plasmid with a 5.2-kilobase (kb) PstI-SalI fragment was found to overproduce 3-hydroxyacyl-coenzyme A (CoA) epimerase and delta 3-cis-delta 2-trans-enoyl-CoA isomerase as well as three other beta-oxidation enzymes by 16- to 18-fold compared with the wild-type parental strain LE392. The purification of a fully functional multienzyme complex of fatty acid oxidation from the transformant ultimately established that the 5.2-kb DNA fragment contained an entire fadAB operon. Since immunotitration of cell extracts with antibodies against the fatty acid oxidation complex proved that all 3-hydroxyacyl-CoA epimerase and delta 3-cis-delta 2-trans-enoyl-CoA isomerase activities were associated with the complex, no genetic loci other than the fadAB operon encoded these two enzymes. Moreover, the binding of antibodies caused parallel inhibition of four component enzymes, whereas 3-ketoacyl-CoA thiolase activity was slightly increased. These findings support the suggestion that the epimerase and isomerase as well as enoyl-CoA hydratase and L-3-hydroxyacyl-CoA dehydrogenase are located on the same polypeptide. The results of this study, together with published data (S.-Y. Yang and H. Schulz, J. Biol. Chem. 258:9780-9785, 1983), lead to the conclusion that 3-hydroxyacyl-CoA epimerase, delta 3-cis-delta 2-trans-enoyl-CoA isomerase, and enoyl-CoA hydratase in addition to 3-hydroxyacyl-CoA dehydrogenase are encoded by the fadB gene.

3-Hydroxyacyl CoA Dehydrogenases↗

PubMed1988