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Biomedical subjects

Z Y Li

Publications and source records attributed to Z Y Li.

At least 55 records · Page 3Linked to original sources
PubMed2000

Microbial transformation of 2-hydroxy and 2-acetoxy ketones with Geotrichum sp.

Biotransformation of a series of o-, m- and p-substituted alpha-hydroxy- and alpha-acetoxyphenylethanones 1a-h and 9a-g with Geotrichum sp. led to the corresponding 1,2-diols 2 and/or monoacetates 10 in moderate to excellent enantiomeric excesses. Alpha-hydroxy- and alpha-acetoxyphenylethanones and their m- and p-derivatives gave preponderantly the S-configuration products while in the case of the o-derivatives R-alcohol was provided as the major enantiomer. The results of stereoselectivity were discussed.

Biotransformation↗
PubMed2000

Cloned piglets born after nuclear transplantation of embryonic blastomeres into porcine oocytes matured in vivo.

Nuclear transplantation in the pig is more difficult than in other domestic animals and only one embryonic nuclear transplantation (NT) pig has been born to date. In this study, reconstituted porcine embryos were produced by electrofusion of blastomeres from in vivo four-cell embryos to enucleated in vivo or in vitro matured (IVM) oocytes. Nuclear transfer using cumulus cells as nuclear donors was also conducted. When blastomeres were used as donors, the electrofusion rate was significantly higher in oocytes matured in vivo (91.5%) than in those matured in vitro (66.1%) (p < 0.01). After fusion, the NT embryos reconstituted from in vivo matured oocytes developed to blastocysts at a rate of 10.3% after culture in rabbit oviducts for up to 5 days, while only 5.9% of the NT embryos reconstructed from in vitro matured oocytes developed to blastocyst stage. Electrofusion rate of cumulus cell nuclei with enucleated IVM oocytes was lower (47.6%) and only 1.5% (2/136) of the reconstituted eggs developed in vitro to morula stage, and 1.9% developed to blastocysts when cultured in the ligated rabbit oviducts. Transfer of 94 embryos reconstructed by blastomere NT with in vivo matured oocytes to five synchronous recipients resulted in the birth of two cloned piglets. No piglet was born following transfer to two recipients of embryos (n = 39) derived from NT with in vitro matured oocytes. The results demonstrate that in vivo matured oocytes are better recipients than those matured in vitro for pig cloning.

Animals↗
PubMed2000

A rapid method for determining the G+C content of bacterial chromosomes by monitoring fluorescence intensity during DNA denaturation in a capillary tube.

A simple and rapid method to determine the G+C content of bacterial chromosomal DNA was developed. It involves determination of Tm by a Light Cycler and calculation of the G+C content by an empirical formula relating Tm to G+C content. Instead of a conventional thermal denaturation method, which monitors the increase of absorbance at 260 nm, thermal denaturation was monitored by the decrease of fluorescence intensity in the presence of SYBR Green 1. In this method, the apparent Tm of DNA was influenced by the concentration of SYBR Green 1, DNA and salt. In addition, when the G+C content was calculated from a linear equation [(mol% G+Cx = mol% G+Cr+1.99(Tmx-Tmr), where x is the unknown organism and y is the reference organism], an error value was introduced among strains with extremely low or high G+C content. Based upon five standards (G+C contents in the range 33-66 mol%), a suitable equation was formulated for the capillary method: mol% G+Cx = mol% G+Cr+1.4652(Tmx-Tmr)+0.0063(Tmx2-Tmr2). To determine the Tm of organisms within this range of G+C contents, Escherichia coli ATCC 11775T was used as a DNA standard and fixed concentrations of SYBR Green 1, sodium citrate and DNA were used. The data from 37 bacterial strains indicated that this equation behaved well. Because it is rapid and simple, it may prove useful for bacterial identification.

Bacteria↗
PubMed2000

Assisted folding of D-glyceraldehyde-3-phosphate dehydrogenase by trigger factor.

The Escherichia coli trigger factor is a peptidyl-prolyl cis-trans isomerase that catalyzes proline-limited protein folding extremely well. Here, refolding of D-glyceraldehyde-3-phosphate dehydrogenase (GAPDH) in the presence of trigger factor was investigated. The regain of activity of GAPDH was markedly increased by trigger factor after either long- or short-term denaturation, and detectable aggregation of GAPDH intermediates was prevented. In both cases, time courses of refolding of GAPDH were decelerated by trigger factor. The reactivation yield of GAPDH showed a slow down-turn when molar ratios of trigger factor to GAPDH were above 5, due to tight binding between trigger factor and GAPDH intermediates. Such inactive bound GAPDH could be partially rescued from trigger factor by addition of reduced alphaLA as competitor, by further diluting the refolding mixture, or by disrupting hydrophobic interactions in the complexes. A model for trigger factor assisted refolding of GAPDH is proposed. We also suggest that assisted refolding of GAPDH is due mainly to the chaperone function of trigger factor.

Enzyme Activation↗
PubMed2000

Nuclear import of moloney murine leukemia virus DNA mediated by adenovirus preterminal protein is not sufficient for efficient retroviral transduction in nondividing cells.

Moloney murine leukemia virus (MoMLV)-derived vectors require cell division for efficient transduction, which may be related to an inability of the viral DNA-protein complex to cross the nuclear membrane. In contrast, adenoviruses (Ad) can efficiently infect nondividing cells. This property may be due to the presence of multiple nuclear translocation signals in a number of Ad proteins, which are associated with the incoming viral genomes. Of particular interest is the Ad preterminal protein (pTP), which binds alone or in complex with the Ad polymerase to specific sequences in the Ad inverted terminal repeat. The goal of this study was to test whether coexpression of pTP with retroviral DNA carrying pTP-binding sites would facilitate nuclear import of the viral preintegration complex and transduction of quiescent cells. In preliminary experiments, we demonstrated that the karyophylic pTP can coimport plasmid DNA into the nuclei of growth-arrested cells. Retroviral transduction studies were performed with G(1)/S-arrested LTA cells or stationary-phase human primary fibroblasts. These studies demonstrated that pTP or pTP-Ad polymerase conferred nuclear import of retroviral DNA upon arrested cells when the retrovirus vector contained the corresponding binding motifs. However, pTP-mediated nuclear translocation of MoMLV DNA in nondividing cells was not sufficient for stable transduction. Additional cellular factors activated during S phase or DNA repair synthesis were required for efficient retroviral integration.

Adenoviruses, Human↗
PubMed2000

Identification and chromosomal localization of a transcriptionally active retrotransposon of Ty3-gypsy type in rice.

A DNA fragment representing a transcriptionally active retrotransposon of Ty3-gypsy type was isolated and characterized from rice (Oryza sativa L.). The fragment (named RIRE9) includes the coding sequences for the C-terminal part of the RNase H domain and the N-terminal part of the integrase domain in the polyprotein region. Northern blot hybridization indicated that this element was expressed in rice leaves and stems, suggesting that it is potentially active to transpose under normal growth conditions. Using dot-blot hybridization, the copy number of RIRE9 was estimated to be about 1600 copies per haploid rice genome. Five homologous copies of RIRE9 were assigned to five distinct positions of four chromosomes by restriction fragment length polymorphism (RFLP) mapping approach using an indica-japonica rice doubled-haploid (DH) population and its molecular linkage map.

Amino Acid Sequence↗
PubMed2000

Expression of N-deacetylase/sulfotransferase and 3-O-sulfotransferase in rat alveolar type II cells.

Basal laminae beneath alveolar type I cells are suggested to contain highly sulfated heparan sulfate-containing proteoglycans (PGs), and cultured type II cells accumulate highly sulfated matrices. To characterize the regulation of PG synthesis during the transition from type II cells to type I cells, we examined mRNA expression of N-deacetylase/sulfotransferase (NST) and 3-O-sulfotransferase (3-OST), two enzymes specific for heparan sulfate synthesis. We found that both freshly isolated and cultured type II cells expressed NST and 3-OST as shown by in situ hybridization. Expression of surfactant-associated protein A, B, and C mRNAs, determined by semiquantitative PCR, decreased during culture. Expression of type I cell marker T1alpha mRNA increased except in cells cultured on an Engelbrecht-Holm-Swarm gel. Expression of NST was dependent on cell density and matrix and was intense in conditions where cells spread fully, whereas 3-OST expression was unchanged in the conditions examined. The PG sulfation inhibitor sodium chlorate significantly inhibited cultured type II cell spreading, and this inhibition was reversed by sodium sulfate. These results suggest that highly sulfated PGs modified by NST are necessary for the spreading of cells during transdifferentiation of type II cells to mature type I cells.

Amidohydrolases↗
PubMed2000

[Study of the factors of Cr(III) bioaccumulation on Spirulina platensis].

Some factors of Cr(III) bioaccumulation on Spirulina platensis were studied in detail. It was found that the bioaccumulation of Cr(III) on Spirulina platensis involved two steps: rapid adsorption and slow absorption. Chromic(III) compounds with weaker chemical bond had higher bioaccumulation efficiency. Under the same algal cell concentration, Cr(III) bioaccumulation rosed up with Cr(III) concentration. On the other hand, with Cr(III) concentration not changed, the total bioaccumulation of Cr(III) on Spirulina platensis increased with algal cell concentration, but the Cr(III) bioaccumulation on unit algae reduced. The study also showed that Spirulina platensis powder could bioaccumulate more Cr(III) than fresh Spirulina platensis, pH is a quite important factor and more suitable pH for Cr(III) bioaccumulation is 7. It was also proved that Cr(III) bioaccumulation benefited from the increase of temperature and light intensity. Cations had either stimulation or inhibition effects on the Cr(III) bioaccumulation on Spirulina platensis.

Bacterial Proteins↗
PubMed2000

[The vagus nerve coordinates the motion of gallbladder and sphincter of Oddi in the interdigestive period in rabbits].

AIM: To investigate the effect of vagus nerve on coordinating the motion of gallbladder (GB) and sphincter of Oddi (SO) in the interdigestive period in rabbits. METHODS: Fasted for 15 h-18 h, but allowed to drink water, the rabbib were anesthetized with urethane (1.0 mg/kg, i.v.). In order to measure GB pressure, a frog bladder filled with normal saline was put into GB and connected to a transducer (TP-200T). Myoelectric signals of SO was recorded by a pair of copper electrodes. RESULTS: In the interdigestive period, phasic contractions of GB (PCGB) and clusters of spike potentials of SO (CSPSO) was 1:1 correlated (Y = 0.962X + 0.587, r = 0.982, P < 0.01). That is, every PCGB was accompanied by one CSPSO. Microinjection of thyrotropin-releasing hormone (TRH, 0.8 nmol, 1 microliter) or monosodium glutamate (MSG, 2 mumol, 1 microliter) into dorsal vagal complex (DVC) enhanced the motility of GB and SO, and the 1:1 temporal relation between PCGB and CSPSO still existed. Vagotomy or intravenous injection of atropine inhibited the PCGB and the spike potentials of SO, and the 1:1 correlation between PCGB and CSPSO disappeared. The spike bursts of SO did not respond to the artificial rise of gallbladder pressure. CONCLUSION: In the interdigestive period in rabbits, gallbladder and SO contract and relax rhythmically and simultaneously. This eoordinated motion between GB and SO is controlled by DVC via vagus nerve and peripheral M receptors.

Animals↗
PubMed2000

[Repairing of soft tissue defect in leg by free vascularized thoracoumbilical flap with reversed flow].

OBJECTIVE: To investigate the clinical effect of free vascularized thoracoumbilical flap with reversal flow in repairing the soft tissue defect in leg with tibia exposure. METHODS: Forty-four casting mould specimens of leg arteries were studied firstly. Then 25 cases with soft tissue defect and tibia exposure in the proximal-middle segment of leg were adopted in this study. Among them, 18 cases had long distance thrombosis of the anterior tibial vessels or posterior tibial vessels due to traumatic lesion. The maximal size of defect was 28 cm x 11 cm and the minimal size of defect was 11 cm x 9 cm. In operation, the thoracoumbilical flap which was based on the inferior epigastric vessels was anastomosed to the distal end of the anterior tibial vessels or posterior tibial vessels. RESULTS: Anterior tibial artery, posterior tibial artery and fibular artery had rich communication branches in foot and ankle. All the flaps survived, the color and cosmetic result of them were good. CONCLUSION: The free vascularized thoracoumbilical flap with reversed flow is practical in repairing the soft tissue defect of leg with tibia exposure. Either the anterior tibial vessels or the posterior tibial vessels is normal, and the distal end of injured blood vessels is available, this technique can be adopted.

Adolescent↗
PubMed2000

[Protein kinase B and its role in the signal transduction pathway mediated by phosphoinositide 3-kinase].

Protein kinase B (PKB) is the expression product of a proto-oncongen (c-akt), which is involved in the signaling pathways initiated by some growth factors and mediated by phosphoinositide 3-kinase (PI3K). PKB is a direct target of PI3K. Similar to many protein kinases, PKB has a specific AH/PH domain which can mediate the interaction between signaling molecules. The lipid second messengers, PI-3, 4-P2 and PI-3,4,5-P3 produced by PI3K, can bind to the AH/PH domain of PKB and of PDK (phosphoinositide dependent protein kinase). This binding translocates PKB and PDK to the plasma membrane, and activates them. PKB is also activated via phosphorylation by PDK and, in turn, will activate the anti-apoptotic machinery, glucose metabolism (glycogen synthesis, glycolysis and glucose uptake) and protein synthesis. All these lead to cell growth and proliferation.

3-Phosphoinositide-Dependent Protein Kinases↗
PubMed1999

[Studies on microinjection of mouse spermatozoa into rabbit oocytes].

The methods of intracytoplasmic sperm injection (ICSI) and subzonal injection (SUZI) were used to study heterologous fertilization and embryonic development between the mouse and the rabbit. Results were as follows: 1. The mouse sperm nuclei decondensed and formed pronuclei following microinjection into cytoplasm and perivitelline space (PVS) of rabbit oocytes; 2. The hybrid embryos developed to the stage of 8-cell when cultured in vitro; 3. The karyotype analysis showed a normal complement of rabbit oocyte and mouse sperm chromosomes in the 4-cell hybrid embryos; 4. The ultrastructure of 4-cell hybrid embryos was similar to that of normal 4-cell rabbit embryos; 5. The fertilization rate (32.4%) and cleavage rate (22.2%) when 5-10 mouse spermatozoa were injected were higher than those of injection of a single spermatozoon into PVS of the rabbit oocyte, but the difference was not significant (P > 0.05). The fertilization rate (42.3%) and cleavage rate (30.8%) in rabbit oocytes in vitro matured for 11-12 h were higher than those in the oocytes which were in vitro matured for 24-25 h following microinjection of 1-2 mouse spermatozoa into PVS, but the difference was not significant (P > 0.05).

Animals↗
PubMed1999

[RAPD method for the identification of intergeneric asymmetric somatic hybrid plants of wheat].

Randomly amplified polymorphic DNA (RAPD) method was used to identify the hybrid nature of three kinds of intergeneric asymmetric somatic hybrid plants of wheat: wheat (Triticum aestivum) + Haynaldia villosa, Wheat + Leymus chinensis and wheat + Agropyron elongatum. It was shown from the electrophoresis profiles that the genome of somatic hybrid plants contained specific section genome of both parents after DNA amplification with arbitrary primers. A specific RAPD product (DNA fragment of 0.77 kbp) of A. elongatum generated with primer OPJ-12 was isolated, purified, labeled and used as a probe. Southern blot from OPJ-12 primer-generated specific section genome of the hybrid (T. aestivum + A. elongatum) hybridized to this probe (0.77 kbp) proved that they are homologous in nature. This paper also discussed the advantage of RAPD method in identification of hybrid plants, especially asymmetric somatic hybrids.

Genome, Plant↗
PubMed1998

Activation of dihydrofolate reductase following thiol modification involves a conformational change at the active site.

Compared with the activation of dihydrofolate reductase (DHFR) by protein denaturants and inorganic salts, activation of the enzyme by thiol modification is relatively slow. Thus it is an ideal system for kinetic study of the activation mechanism. We describe here a kinetic study of the activation of DHFRs from chicken liver and Chinese hamster ovary by p-hydroxymercuribenzoate (p-HMB). The conformational changes in the enzyme molecule that result from the modification were monitored by measuring fluorescence enhancement due to the binding of 2-p-toluidinylnaphthalene-6-sulphonate (TNS), and by monitoring changes in the intrinsic fluorescence of the enzyme. Both activation and the conformational change probed by TNS followed pseudo-first-order kinetics, and the rate constants obtained are in good agreement with each other. The change in intrinsic fluorescence is a biphasic process. The rate of the fast phase, which may reflect a change in the microenvironment of Trp-24 at the active site, coincides with the rate of activation and the conformational change probed by TNS. The rate of the slow phase, which reflects a global conformational change, is about one order of magnitude lower than that of activation. The results indicate that the activation of DHFR by p-HMB is due to modification-induced conformational changes at its active site, rather than the modification of the thiol group itself, which is almost complete within the dead-time of the experiment. This study provides kinetic evidence for the proposal that flexibility at the active site is essential for full expression of catalytic activity.

Animals↗
PubMed1998

Disease sequence from mutant rhodopsin allele to rod and cone photoreceptor degeneration in man.

Mutations in the gene encoding rhodopsin, the visual pigment in rod photoreceptors, lead to retinal degeneration in species from Drosophila to man. The pathogenic sequence from rod cell-specific mutation to degeneration of rods and cones remains unclear. To understand the disease process in man, we studied heterozygotes with 18 different rhodopsin gene mutations by using noninvasive tests of rod and cone function and retinal histopathology. Two classes of disease expression were found, and there was allele-specificity. Class A mutants lead to severely abnormal rod function across the retina early in life; topography of residual cone function parallels cone cell density. Class B mutants are compatible with normal rods in adult life in some retinal regions or throughout the retina, and there is a slow stereotypical disease sequence. Disease manifests as a loss of rod photoreceptor outer segments, not singly but in microscopic patches that coalesce into larger irregular areas of degeneration. Cone outer segment function remains normal until >75% of rod outer segments are lost. The topography of cone loss coincides with that of rod loss. Most class B mutants show an inferior-nasal to superior-temporal retinal gradient of disease vulnerability associated with visual cycle abnormalities. Class A mutant alleles behave as if cytotoxic; class B mutants can be relatively innocuous and epigenetic factors may play a major role in the retinal degeneration.

Adult↗
PubMed1998

Histopathology of the human retina in retinitis pigmentosa.

The term, 'retinitis pigmentosa', refers to a heterogeneous group of inherited diseases that cause degeneration of rod and cone photoreceptors in the human retina. Loss of photoreceptor cells is usually followed by alterations in the retinal pigment epithelium and retinal glia. Ultimately, degenerative changes occur in the inner retinal neurons, blood vessels, and optic nerve head. This chapter provides background information on the genetics of retinitis pigmentosa and a summary of the histopathologic alterations in human retinas caused by this disease. Detailed information is provided on the effects of the primary disease process on the rod photoreceptors and changes in the other retinal components, all of which are important considerations for understanding and developing therapies for retinitis pigmentosa.

Astrocytes↗
PubMed1998

Removal of a dimeric form of surfactant protein C from mouse lungs: its acceleration by reduction.

Clearance of hydrophobic surfactant-associated protein C (SP-C) and its dimeric form ([SP-C]2) was investigated. SP-C and [SP-C]2 obtained from proteinosis patients were fluorescently labeled and were instilled into mouse lungs as lipid-protein complexes. [SP-C]2 was removed more slowly than SP-C, with apparent half-lives of 30 and 18 h, respectively. A significant amount of [SP-C]2 was removed as SP-C, and the conversion rate was 0.22 micrograms.h-1.mouse-1. By correcting the removal as SP-C, we obtained 38 h for a possible half-life of [SP-C]2. Conversion from SP-C to [SP-C]2 seemed very slow. Decrease in glutathione (GSH) in the lung inhibited the conversion of [SP-C]2 to SP-C and GSH-treatment of liposomes accelerated clearance of [SP-C]2. These results suggest that the removal of [SP-C]2 from lung is accelerated by reduction and that GSH acts as a reducing agent in the lung.

Animals↗