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Biomedical subjects

Z Xie

Publications and source records attributed to Z Xie.

At least 199 records · Page 11Linked to original sources
PubMed1997

[Purification and properties of inulinase from Kluyveromyces sp. Y-85].

The crude endocellular inulinase from Kluyveromyces sp. Y-85 was purified to two components, designated as EI and EII, using PEG6000-phosphate buffer extraction, (NH4)2SO4 fractionation, DEAE chromatography and gel filtration (Protein-PAK); The crude exocellular inulinase from this strain was purified to Eexo by means of PEG6000-phosphate buffer extraction, double DEAE-Sephace chromatography, Sephadex G-150 gel filtration. EI, EII and Eexo were demonstrated to be homogeneous by Waters 650E protein purification system. Their molecular weights are 42 kD, 65 kD and 57 kD, respectively. All the inulinases were glycoproteins containing a saccharide (from 25% to 35%) and belonged to the endo-inulinase. In addition, EI, EII, Eexo were optimally reactive at pH4.6, 4.5, 4.6 and at 52 degrees C, 52 degrees C, 55 degrees C, respectively. Ag+, Hg2+ and PCMB inhibited these enzymes' activity strongly. The products of raw inulin extracted from Helianthus tuberosus hydrolyzed by these three enzymes were fructose (86.5%) and glycose (13.5%).

English Abstract↗
PubMed1997

Isotypic antibody responses of a population in an endemic area of schistosomiasis japonica and their epidemiologic significance.

The present study was designed to explore if there exists a correlation between predominant isotype-defined antibody levels and reinfection in low age groups of the population in an endemic area of schistosomiasis japonica in China. One hundred and thirty-eight individuals aged 3-25 years old were selected for serological investigations including the levels of IgG, IgG4, IgM and IgE, detected by ELISA with soluble egg antigen and soluble adult worm antigen. Results show that age is a determinant for SEA-specific IgG, IgG4, and IgE, and SWA-specific IgG and IgG4 antibody levels, which increased with age, and that SEA- and SWA- specific IgG4 antibody levels are risk factors of reinfection, ie, the risk of reinfection occurrence of the population with high level of SEA or SWA-specific IgG4 is 2.83 or 2.40 times, respectively, that with low level of SEA or SWA-specific IgG4, suggesting that in the endemic area of schistosomiasis japonica, there exists a possibility that in the population aged 3-25 years, SEA and SWA-specific IgG4 antibodies mediate a blocking immunity response.

Adolescent↗
PubMed1997

[Voltage-dependent potassium currents in rat C6 glioma cells].

In the present study, the properties of voltage-dependent K- currents in cultured rat C6 glioma cells were investigated with the whole cell patch-clamp recording technique. A total of 97 cells were recorded. The mean value of the membrane potential was -47.5 +/- 9.4 mV. Seven percent of the recorded C6 glioma cells did not show any outward potassium currents. The rest had outward K+ currents which could be activated at -36.5 +/- 5.9 mV from a holding potential of -70 mV. Ananalysis of tail currents, showed the mean value of the reversal potential was -84.6 +/- 4.1 mV, close to the K+ equilibrium potential. The K+ currents of 60% of the recorded C6 cells consisted of both a fast and a slow component, while those of the 33% only with a slow component.

Animals↗
PubMed1997

[Inhibition of voltage-dependent K+ currents in rat C6 glioma cells by haloperidol and R(-)-NPA].

In this study, the inhibitory effects of R(-)-NPA (R(-)-Propylnorapomorphine) and haloperidol on voltage-dependent K+ currents in rat C6 glioma cells (C6 cells) were observed by means of the whole-cell patch-clamp recording technique. The mechanisms of the effects were also analyzed. The main results were as follows: (1) Both R(-)-NPA and haloperidol could inhibit K+ currents dose-dependently and reversibly in C6 cells. (2) R(-)-NPA and haloperidol inhibited mainly the slow component of the K+ currents. (3) These inhibitory responses were not mediated by dopamine receptors or dependent on G-proteins and intracellular calcium. It was suggested that they refer to some direct action on K+ channels.

Animals↗
PubMed1997

[Histological study on the using of autogenous costal perichondrium graft to repair the cartilage of condylar process of mandible].

In order to observe the histological changes of the autogenous perichondrium graft from rib in the repair of injured articular cartilage of the condylar process of mandible, 50 rabbits were used, in which 15 were served as control. The articular cartilage with its subchondral bone were resected and an autogenous graft of costal perichondrium was sutured onto the raw surface of the condylar process, and in the controls, only the articular portion of the condylar process was resected without the application of autogenous costal perichondrium graft. The morphological changes of the newly formed cartilage during the process of its development were investigated by hiostological and autoradiog aphic techniques. The result revealed that 10 days after operation, the graft had increased in thickness and was richly populated form the proliferation of mesenchyme-like cells. Twenty to thirty days later, the chondrocytes were matured and the newly formed cartilage had covered the bony surface of mandibular condyle. At 60 days, the newly formed cartilagenous joint surface became glossy, and the morphology and arrangement of cells tended to be regular simulating the morphology of normal articular cartilage. From the experiment, it could be concluded that (1) The autogenous perichondrium graft placed on the condylar surface of mandible could form new articular cartilage which was similar in tissue morphology to the normal condylar cartilage. (2) The process of development of newly formed cartilage was similar to that of the normal cartilage. (3) The motion and loading on the joint could promote the formation of new cartilage and undergo biological reformation, gradually resulting in normal joint morphology. On this basis, the clinical application of autogenous perichondrium graft to repair injured cartilage of the condylar process of the mandible was feasible.

Animals↗
PubMed1996

JunD phosphorylation, and expression of AP-1 DNA binding activity modulated by serum growth factors in quiescent murine 3T3T cells.

JunD has been implicated as a negative regulator of cell proliferation. If and how JunD is regulated by growth factors however has not been well investigated. We now report that in quiescent murine 3T3T cells, JunD is present in a hypophosphorylated form, but that when quiescent cells are stimulated to proliferate with serum, JunD undergoes a transient increase in its phosphorylation that occurs within 10 min and persists for up to 4 h. The increase in JunD phosphorylation correlates with the induction of cell proliferation since only those growth factors that promote cell proliferation can induce JunD phosphorylation. Treatment of quiescent 3T3T cells with serum also induces significant decreases in JunD/AP-1 DNA binding activity within 2 h and in JunD expression after 8-48h. However, both hypophosphorylated and hyperphosphorylated forms of JunD can bind AP-1 DNA. These results suggest that serum growth factors can modulate JunD characteristics in a variety of apparently independent ways to overcome its negative regulatory effect in controlling cell proliferation. These include induction of a transient increase in JunD phosphorylation, repression of JunD AP-1 DNA binding activity and downregulation of JunD expression.

3T3 Cells↗
PubMed1996

Control of RNA polymerase II elongation potential by a novel carboxyl-terminal domain kinase.

The entry of RNA polymerase II into a productive mode of elongation is controlled, in part, by the postinitiation activity of positive transcription elongation factor b (P-TEFb) (Marshall, N. F., and Price, D. H. (1995) J. Biol. Chem. 270, 12335-12338). We report here that removal of the carboxyl-terminal domain (CTD) of the large subunit of RNA polymerase II abolishes productive elongation. Correspondingly, we found that P-TEFb can phosphorylate the CTD of pure RNA polymerase II. Furthermore, P-TEFb can phosphorylate the CTD of RNA polymerase II when the polymerase is in an early elongation complex. Both the function and kinase activity of P-TEFb are blocked by the drugs 5, 6-dichloro-1-beta-D-ribofuranosylbenzimidazole (DRB) and H-8. P-TEFb is distinct from transcription factor IIH (TFIIH) because the two factors have no subunits in common, P-TEFb is more sensitive to DRB than is TFIIH, and most importantly, TFIIH cannot substitute functionally for P-TEFb. We propose that phosphorylation of the CTD by P-TEFb controls the transition from abortive into productive elongation mode.

Hydrolysis↗
PubMed1996

Restoration of phosphorylation capacity to the dormant half of the alpha-subunits of Na+, K(+)-ATPase.

Purified kidney Na+, K(+)-ATPase whose alpha-subunit is cleaved by chymotrypsin at Leu266-Ala267, loses ATPase activity but forms the phosphoenzyme intermediate (EP) from ATP. When EP formation was correlated with extent of alpha-cleavage in the course of proteolysis, total EP increased with time before it declined. The magnitude of this rise indicated doubling of the number of phosphorylation sites after cleavage. Together with previous findings, these data establish that half of the alpha-subunits of oligomeric membrane-bound enzyme are dormant and that interaction of the N-terminal domain of alpha-subunit with its phosphorylation domain causes this half-site reactivity. Evidently, disruption of this interaction by proteolysis abolishes overall activity while it opens access to phosphorylation sites of all alpha-subunits.

Adenosine Triphosphate↗
PubMed1996

Similarities and differences between the properties of native and recombinant Na+/K+-ATPases.

Progress of mutagenesis studies on the relation of the structure of Na+/K+-ATPase to its reaction mechanism has been impeded by the paucity of information on the properties of small amounts of impure recombinant enzyme obtained in the currently available expression systems, and the uncertainty of whether expression in a new environment alters the various catalytic activities of this membrane enzyme. Hence, our aim was to make a detailed comparison of the properties of the extensively studied canine kidney Na+/K+-ATPase with those of its alpha1,beta1 subunits expressed in the baculovirus-infected Sf-9 cells. The active fraction of the recombinant enzyme, containing 10-20% of the expressed a subunits, was found to have normal molar activity, all the partial reactions, and the ability to catalyze ATP-dependent Na+/K+ exchange after reconstitution into proteoliposomes. Comparison of steady-state kinetics of the hydrolytic activities of recombinant and native enzymes showed that (a) ATP and Na+ plots of Na+-ATPase were the same in the two preparations; (b) apparent K+ affinity of K+-phosphatase of recombinant enzyme was lower than that of kidney enzyme; and (c) for Na+/K+- ATPase activity, apparent K+ affinity of recombinant enzyme was lower, and its apparent Na+ and ATP affinities were higher than those of kidney enzyme. The two enzymes had similar ADP- and K+-sensitive phosphointermediates, identical affinities for ouabain, and similar ligand sensitivities of dissociation rates of ouabain-enzyme complexes. Evidently, the recombinant enzyme has reduced affinity at cytoplasmic K+ sites, but no changes at multiple Na+, ATP, and ouabain binding sites. Likely causes of this selective change include altered glycosylation state of beta and interactions among active and inactive recombinant enzymes. The present results provide the necessary database for the appropriate use of an expression system in structure-function studies on canine alpha1,beta1 isoform of Na+/K+-ATPase, and indicate the need for similar studies on recombinant Na+/K+-ATPases obtained in other expression systems.

Animals↗
PubMed1996

Purification of an RNA polymerase II transcript release factor from Drosophila.

Factor 2 was previously identified in Drosophila Kc cell nuclear extract (KcN) as an activity suppressing the appearance of long transcripts (Price, D. H., Sluder, A. E., and Greenleaf, A. L. (1987) J. Biol. Chem. 262, 3244-3255). A 154-kDa protein with factor 2 activity was purified to apparent homogeneity from KcN. An immobilized template assay indicated that factor 2 caused the release of transcripts by RNA polymerase II in an ATP-dependent manner. Some early elongation complexes were resistant to factor 2 action but became sensitive after treatment with 1 M KCl. In the absence of factor 2, transcription complexes still exhibited a low degree of processivity suggesting that factor 2 was only partially responsible for abortive elongation.

Adenosine Triphosphatases↗
PubMed1996

Partial inhibition of Na+/K+-ATPase by ouabain induces the Ca2+-dependent expressions of early-response genes in cardiac myocytes.

Exposure of neonatal rat cardiac myocytes to ouabain concentrations that caused partial inhibition of Na+/K+-ATPase but no loss of viability, increased c-fos and c-jun mRNAs and the transcription factor AP-1. The increased mRNAs were proportional to the extent of inhibition of Na+/K+-ATPase and the resulting rise in steady state intracellular Ca2+ concentration. The rapid and sustained increase of c-fos mRNA was shown to be due to increased transcriptional rate. Induction of c-fos by ouabain was prevented when either extracellular or intracellular Ca2+ was lowered and was attenuated by pretreatment of myocytes with a phorbol ester under conditions known to down-regulate protein kinase C. Exposure to ouabain for 24-48 h also increased total transcriptional activity and protein content of myocytes. The findings suggest that the same signal responsible for the positive inotropic action of ouabain, i.e. net influx of Ca2+ caused by partial inhibition of Na+/K+-ATPase, also initiates the rapid protein kinase C-dependent inductions of the early-response genes, the subsequent regulations of other cardiac genes by the resulting transcription factors, and stimulation of myocyte growth. Whether these hitherto unrecognized effects of cardiac glycosides are obtained in the intact heart and their relevance to the therapeutic uses of these drugs remain to be determined.

Animals↗
PubMed1996

The plastid-encoded ccsA gene is required for heme attachment to chloroplast c-type cytochromes.

A chloroplast gene, ycf5, which displays limited sequence identity to bacterial genes (ccl1/cycK) required for the biogenesis of c-type cytochromes, was tested for its function in chloroplast cytochrome biogenesis in Chlamydomonas reinhardtii. Targeted inactivation of the ycf5 gene results in a non-photosynthetic phenotype attributable to the absence of c-type cytochromes. The cloned ycf5 gene also complements the phototrophic growth deficiency in strain B6 of C. reinhardtii. B6 is unable to synthesize functional forms of cytochromes f and c6 owing to a chloroplast genome mutation that prevents heme attachment. The selected (phototrophic growth) as well as the unselected (holocytochrome c6 accumulation) phenotypes were restored in complemented strains. The complementing gene, renamed ccsA (for c-type cytochrome synthesis), is expressed in wild-type and B6 cells but is non-functional in B6 owing to an early frameshift mutation. Antibodies raised against the ccsA gene product recognize a 29-kDa protein in C. reinhardtii. The 29-kDa protein is absent in strain B6 but is restored in a spontaneous revertant (B6R) isolated from a culture of B6. Sequence analysis of the ccsA gene in strain B6R indicates that it is a true revertant. We conclude that the ccsA gene is expressed and that it encodes a protein required for heme attachment to c-type cytochromes.

Amino Acid Sequence↗
PubMed1996

Activation of Na+/K(+)-ATPase by fatty acids, acylglycerols, and related amphiphiles: structure-activity relationship.

A number of fatty acids and derivatives have been shown to activate Na+/K(+)-ATPase when ATP is suboptimal. To explore the relation of the structures of these amphiphiles to enzyme activation, the effects of varying amphiphile concentrations on the activity of the highly purified kidney Na+/K(+)-ATPase at 50 microM ATP were determined. Among fatty acids, efficacy (maximal level of activation) and potency were found to be dependent, in different ways, on chain length and unsaturation. Compared to fatty acids, the corresponding alcohols had lower efficacies. Methyl esters of fatty acids inhibited, but CoA esters and monoacyl esters of glycerol activated the enzyme. Relation between chain length and potency among CoA esters and monoacylglycerols was the same as that observed with acids. Diacylglycerols did not activate, but they antagonized the effects of the activator amphiphiles. The substantial specificities of the amphiphile effects support the hypothesis that these ligands bind to a distinct amphipathic peptide segment of the intracellular central loop of the alpha-subunit to regulate ATP binding to the enzyme. The findings also suggest that direct effects of the changing intracellular levels of fatty acids and derivatives on Na+/K(+)-ATPase should be considered as a possible mechanism for the regulation of its function in the intact cell.

Animals↗
PubMed1996

Multiple within-day conflict testing to define the time course of anxiolytic drug effects.

The present article describes a method for multiple within-day conflict testing to conduct drug treatment time course studies more efficiently. Groups of female Sprague-Dawley rats were trained for conflict testing in a standard one-session/day procedure [conditioned suppression of drinking (CSD)]. In this task, thirsty rats (24 h water-restricted) drink from a tube that is electrified only when a tone is on (approximately 20% of the 10-min session time). In Experiment 1 it was found that there was no significant variation in CSD conflict behavior when subjects were tested at 0600, 1200, or 1800 h using the traditional procedure of one test/day. In Experiment 2, subjects were assigned to treatment groups such that there were three 5-min test sessions per day and the test-retest interval was either 2, 4, or 6 h (centered around 1200 h). Test-retest intervals of 6 h (i.e., tests at 0600, 1200, and 1800 h) resulted in comparable levels of punished responding across the repeated within-day tests, whereas test-retest intervals of 2 h and, to a lesser extent 4 h, resulted in unequal within-day conflict behavior characterized by a greater number of shocks accepted and a greater volume of water consumed during the earliest test periods each day. In another group of rats, it was determined that conflict behavior sampled five times/day in 3-min sessions separated by a 3-h test-retest interval (i.e., tests at 0600, 0900, 1200, 1500, and 1800 h) also resulted in stable conflict behavior across the various within-day test periods. In Experiment 3, it was found that acute IP challenges with anticonflict treatments that exhibit either a long duration of action (phenobarbital: 40 mg/kg) or a significant delay to onset in addition to a long duration (MK-801: 0.20 mg/kg) yielded time course data comparable to those obtained using the traditional one test/day procedure. These findings indicate that the use of multiple within-day conflict testing can greatly increase the efficiency of these procedures, particularly when drug treatment timecourse information is desired.

Animals↗
PubMed1996

Differentiation modulates the balance of positive and negative Jun/AP-1 DNA binding activities to regulate cellular proliferative potential: different effects in nontransformed and transformed cells.

Differentiation of 3T3T cells into adipocytes results in the progressive repression of growth factor responsiveness. This is associated with the transcriptional repression of the inducibility of c-jun and junB expression by serum. In contrast, differentiation of SV-40 large T antigen-transformed 3T3T cells (CSV3-1) does not repress growth factor responsiveness nor c-jun or junB inducibility even though CSV3-1 cells can differentiate into adipocytes. To better explain these observations, we have studied compositional changes in AP-1 DNA binding activity attributed to c-Jun, JunB, and JunD during the differentiation process in 3T3T and CSV3-1 cells. The results show that in nontransformed 3T3T cells, differentiation represses AP-1 DNA binding activity via a proportionate downregulation of c-Jun, JunB, and JunD. In contrast, in CSV3-1 cells, AP-1 DNA binding activity increases twofold during differentiation, which is accounted for by an increase in JunD with no change in c-Jun and JunB. If c-Jun and JunB serve as positive regulators and JunD serves as a negative regulator for cell proliferation as suggested by previous studies, the repression of JunD expression in differentiating CSV3-1 cells should be mitogenic because decreasing JunD/AP-1 DNA binding activity would allow c-Jun/AP-1 and JunB/AP-1 DNA binding activities to be dominant. The results confirm this prediction showing that antisense junD oligodeoxyribonucleotides are mitogenic for differentiating CSV3-1 cells whereas antisense c-jun and junB inhibit mitogenesis. These data support the conclusion that differentiation can regulate cellular proliferative potential by modulating the balance of positive and negative Jun/AP-1 DNA binding activities in distinct ways in nontransformed and transformed cells.

3T3 Cells↗