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Y Xu

Publications and source records attributed to Y Xu.

At least 1,117 records · Page 62Linked to original sources
PubMed1993

Small-volume voltammetric detection of 4-aminophenol with interdigitated array electrodes and its application to electrochemical enzyme immunoassay.

A small-volume voltammetric detection of 4-aminophenol (PAP) has been developed using an interdigitated array (IDA) microelectrode cell in order to apply the IDA to electrochemical enzyme immunoassay. The signal of PAP at the IDA was steady state, and its magnitude was amplified compared with that of the usual single electrode due to redox cycling of PAP between the two finger sets of the IDA. A linear relationship between PAP concentration and cathodic limiting current was obtained from 1 to 1000 microM, reproducibly. The minimum sample volume in the measurement was reduced to 800 nL. High sample throughput of less than 1-min detection time per sample was achieved on 2-10-microL PAP samples. This IDA cell was applied to the electrochemical enzyme immunoassay of mouse IgG. Alkaline phosphatase was used as the enzyme label. The mouse IgG concentration was evaluated by detecting the concentration of PAP, which is the product of enzymatic reaction of the substrate, 4-aminophenyl phosphate (PAPP). Anti-mouse IgG was covalently immobilized on the glass surface of the small-volume immunowells by carbodiimide coupling. The assay range was 10-1000 ng/mL using 10-microL sample and 20-microL substrate solutions.

Alkaline Phosphatase↗
PubMed1993

Inhibition of tobacco-specific nitrosamine-induced lung tumorigenesis by compounds derived from cruciferous vegetables and green tea.

We have shown that PEITC and I3C, both of cruciferous origin, inhibited lung tumor formation induced by the tobacco-specific nitrosamine NNK. The inhibition by PEITC is due largely to its inhibitory effect on the enzymes of NNK metabolism, whereas; the inhibition by I3C may be attributed to its ability to induce hepatic enzyme activity of NNK metabolism, which resulted in decreased availability of NNK to the lung. On a molar basis, PEITC is considerably more effective than I3C. PEITC was released upon consumption of watercress. The N-acetylcysteine conjugate of PEITC is a promising urinary marker for quantitating uptake of this dietary anticarcinogen in humans. These studies also showed that green tea polyphenol EGCG inhibited the NNK-induced lung tumorigenesis, probably due to its antioxidant property. These studies provide for the first time evidence for the involvement of free radicals in nitrosamine tumorigenesis. The mechanism by which free radicals are generated by NNK treatment is not yet known. The reduced levels of oxidative lesions in lung as a result of EGCG treatment may be related to its ability to reduce reactive oxygen species and/or to chelate iron ion resulting in a decreased production of hydroxyl radicals. Overall, these studies have identified ingredients in cruciferous vegetables and green tea that are inhibitory against lung tumorigenesis induced by NNK in rodents.

Adenoma↗
PubMed1993

The bacterially expressed yeast CDC34 gene product can undergo autoubiquitination to form a multiubiquitin chain-linked protein.

The CDC34 gene of Saccharomyces cerevisiae encodes a 295-residue ubiquitin-conjugating enzyme (E2). The function of this ubiquitin-conjugating activity remains to be defined as its in vivo substrates are presently unknown. The bacterially expressed and purified Cdc34 protein is shown here to catalyze its own ubiquitination via an intramolecular transfer of its thiol ester-linked ubiquitin to a lysine. In this process, multiple ubiquitin groups are added to Cdc34, and these ubiquitin groups were shown to be arranged predominantly in the form of a single Lys48-specific multiubiquitin chain. Analysis of the hydroxylamine-dependent cleavage of ubiquitin-Cdc34 conjugates at the single Asn-Gly sequence in Cdc34 placed the major ubiquitin linkage site within the C-terminal 215-295 residues of Cdc34. The 4 Lys residues (Lys273, Lys277, Lys293, and Lys294) in this region of CDC34 were substituted by arginine either singly or in combination to produce a set of Cdc34 mutants. Analysis of these Cdc34 mutants for autoubiquitination revealed that the multiubiquitin chain can be formed on any one of these 4 lysines although most Cdc34 conjugates contain a single multiubiquitin chain. Since the presence of a Lys48-specific multiubiquitin chain in protein conjugates is known to target acceptor proteins for degradation in the ubiquitin-mediated proteolytic pathway, the present result raises the possibility that one function of the ubiquitin-conjugating activity in CDC34 may be used to target its own degradation.

Anaphase-Promoting Complex-Cyclosome↗
PubMed1993

Inhibition of tryptophan synthase by (1-fluorovinyl)glycine.

Tryptophan synthase (alpha 2 beta 2 complex) from Salmonella typhimurium catalyzes the formation of tryptophan from serine and indole. The enzyme is inactivated by (1-fluorovinyl)glycine. Concomitant with enzyme inactivation, the absorbance at 485 nm increases, indicating covalent modification of pyridoxal 5'-phosphate. It is proposed that inactivation involves elimination of HF to form an allene, which reacts with a nucleophile at the active site. The inactivation reaction involves an alpha,beta-elimination, as does the formation of tryptophan from indole and serine. The inactivation occurs with k(in) > 1.3 s-1, which is very close to k(cat) (6.4 s-1) for the formation of tryptophan from indole and serine. The inactive enzyme (alpha 2 beta 2) regains activity with k(off) = 0.005 min-1. Aminoacetone is formed during reaction, and pyridoxal 5'-phosphate is regenerated. Tryptophan synthase also catalyzes the dehydration of serine, or 3-fluoroalanine, to pyruvate in the absence of indole. This reaction involves an alpha,beta-elimination and the intermediate formation of an aminoacrylate adduct with pyridoxal 5'-phosphate, as does the formation of tryptophan. Pyruvate formation proceeds at less than 5% the rate of tryptophan formation. With [2-2H]serine an isotope effect (DVmax = 1.5) is observed. We propose that pyruvate formation is limited by the rate of hydration of the aminoacrylate intermediate and the rate of the abstraction of the serine alpha-hydrogen.

Acetone↗
PubMed1993

LH-2: a LIM/homeodomain gene expressed in developing lymphocytes and neural cells.

A screen for early markers of B-lymphocyte differentiation has identified a homeobox gene, denoted LH-2, that has a pattern of expression distinct from that of other related genes. The LH-2 cDNA sequence encodes a polypeptide of 426 amino acids that contains a homeodomain and two repeats of a cysteine-rich domain referred to as a LIM domain. The homeodomain of the LH-2 protein is related to that of other LIM/homeodomain proteins, most strikingly with that of the Drosophila apterous protein. Expression of LH-2 was found in B- and T-lymphoid cell lines. Expression in B-cell lines was highest in lines that represent early stages of differentiation, whereas in T-cell lines there was no clear correlation with the stage of differentiation. In embryonic and adult tissues, the highest level of LH-2 expression was found in discrete regions of the developing central nervous system, primarily in diencephalic and telencephalic structures, and in a subset of lymphoid tissues. The expression pattern and structural characteristics of the LH-2 gene suggest that it encodes a transcriptional regulatory protein involved in the control of cell differentiation in developing lymphoid and neural cell types.

Aging↗
PubMed1993

B cell development in mice that lack one or both immunoglobulin kappa light chain genes.

We have generated mice that lack the ability to produce immunoglobulin (Ig) kappa light chains by targeted deletion of J kappa and C kappa gene segments and the intervening sequences in mouse embryonic stem cells. In wild type mice, approximately 95% of B cells express kappa light chains and only approximately 5% express lambda light chains. Mice heterozygous for the J kappa C kappa deletion have approximately 2-fold more lambda+ B cells than wild-type littermates. Compared with normal mice, homozygous mutants for the J kappa C kappa deletion have about half the number of B cells in both the newly generated and the peripheral B cell compartments, and all of these B cells express lambda light chains in their Ig. Therefore, homozygous mutant mice appear to produce lambda-expressing cells at nearly 10 times the rate observed in normal mice. These findings demonstrate that kappa gene assembly and/or expression is not a prerequisite for lambda gene assembly and expression. Furthermore, there is no detectable rearrangement of 3' kappa RS sequences in lambda+ B cells of the homozygous mutant mice, thus rearrangements of these sequences, per se, is not required for lambda light chain gene assembly. We discuss these findings in the context of their implications for the control of Ig light chain gene rearrangement and potential applications of the mutant animals.

Animals↗
PubMed1993

TGF-beta 1 induces bone closure of skull defects: temporal dynamics of bone formation in defects exposed to rhTGF-beta 1.

The temporal dynamics of bone repair in a skull defect in rabbits was examined to characterize the in vivo cellular events occurring following a single local application of recombinant human TGF-beta 1 (rhTGF-beta 1). Rabbits received vehicle or 0.4, 1, 2, or 5 micrograms rhTGF-beta 1 applied to 12 mm defects at the time of surgery. The defect sites were subsequently evaluated by radiography and qualitative and quantitative histology at time points ranging from 1 to 180 days. Based on radiographic assessment, the defect area decreased rapidly in a dose-dependent manner through 35 days after surgery in the rhTGF-beta 1-treated groups. Minimal closure occurred in sites administered vehicle control at all time points examined. Sites treated with rhTGF-beta 1 were characterized histologically by an increase in parameters of active bone formation through 49 days, including percentage osteoid surface, percentage osteoblast/total surface, and an increase in the trabecular bone volume. Bone resorption parameters were increased at 16 and 49 days with histologic evidence of remodeling from woven to lamellar bone. By 70 days, no differences were observed among the groups for parameters of either bone formation or resorption. Bone formation rate was not altered with rhTGF-beta 1 treatment at any time point. These results indicate that exogenously applied rhTGF-beta 1 stimulated the recruitment and proliferation of osteoblasts at the defect site, resulting in a rapid deposition of bony matrix, with normal remodeling processes occurring thereafter. This study supports the hypothesis that TGF-beta 1 is a potent osteoinductive growth factor in vivo and may have potential application as a therapeutic aid to nonhealing bony defects.

Animals↗
PubMed1993

Characterization of radioiodinated recombinant human TGF-beta 1 binding to bone matrix within rabbit skull defects.

Bone healing is regulated in part by the local production of TGF-beta 1 and other growth factors produced by cells at the site of injury. The single application of recombinant human TGF-beta 1 (rhTGF-beta 1) to calvarial defects in rabbits induces an accelerated recruitment and proliferation of osteoblasts within 3 days. This ultimately results in the formation of new bone and the complete closure of the defect within 28 days. The persistence and localization of [125I]rhTGF-beta 1 within an osseous defect was investigated after applying a single dose of [125I]rhTGF-beta 1 formulated in a 3% methylcellulose vehicle. Normal bone encompassing the defect site, the periosteum, and the gel film covering the dura were harvested at 0, 4, 8, and 24 h and 3, 7, and 16 days after [125I]rhTGF-beta 1 application. The defect site-associated radioactivity was quantitated, visualized by autoradiography, and characterized by TCA precipitation and SDS-PAGE. Radioactivity was observed in autoradiographs of gross specimens, histologic sections of the bone matrix, and periosteal tissue surrounding the defect. There was a time-dependent decrease in TCA-precipitable radioactivity; however, radioactivity was still associated with the bone matrix 16 days after application of [125I]rhTGF-beta 1. SDS-PAGE and autoradiography of the radioactivity in homogenized bone and periosteal samples revealed a 25 kD band, suggesting that the radioactivity remaining at the defect site represented intact [125I]rhTGF-beta 1.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1993

Nonmagnetic hyperbaric chamber for in vivo NMR spectroscopy studies of small animals.

A description is given of the design, construction, and initial use of a polycarbonate resin hyperbaric chamber for in vivo NMR spectroscopy studies of anesthetized, ventilated rats in a horizontal bore 4.7 Tesla magnet. The chamber and its associated equipment, initially used for hyperbaric studies of rats in states of extreme hypercapnia, are also well suited for conventional hyperbaric studies, such as those related to hyperbaric oxygen therapy, oxygen toxicity, and diving. Basic technical challenges that required innovations involved: a) preservation of magnetic field homogeneity; b) avoidance of a metallic chamber body that would overload gradient and RF coils; c) physiological monitoring; and, d) remote control and stabilization of electromagnetic and physiologic factors (especially ventilatory stability) during pressure changes. A small paramagnetic bulk magnetic susceptibility shift from chamber-associated hyperbaric oxygen was observed when chamber oxygen tensions were only one atmosphere. High-quality NMR imaging and spectroscopy were demonstrated during hyperbaric conditions.

Animals↗
PubMed1993

Responses of myocardial high energy phosphates and wall thickening to prolonged regional hypoperfusion induced by subtotal coronary stenosis.

The response of the myocardium to prolonged or chronic ischemia may differ from the well documented changes that occur acutely subsequent to the onset of hypoperfusion. Therefore, we have examined in an instrumented canine model and using spatially localized spectroscopy to achieve transmural differentiation, the myocardial HEP and Pi levels as well as wall thickening in situ during prolonged ischemia induced by sustained coronary artery stenosis. The results demonstrate that subtotal coronary artery occlusion causes immediate and transmurally inhomogeneous decreases in the myocardial HEP content and increase in the Pi/CP ratio; however, during prolonged mild hypoperfusion, metabolic changes occur which lead to statistically significant recovery of CP (but not ATP) and disappearance of Pi despite the persistence of reduced blood flow and oxygen supply. Upon release of the occlusion, the previously ischemic muscle recovered blood flow, and some (but not all) of its preischemic contractile function without parallel changes in the HEP levels. It is concluded that normal HEP and Pi levels cannot be equated with either the absence of underperfusion or insensitivity of NMR spectroscopy to ischemia. Rather, it is imperative that both functional and spectroscopic measurements are performed simultaneously to distinguish between ischemic myocardium which is adapted versus unadapted to the hypoperfusion.

2,3-Diphosphoglycerate↗
PubMed1993

Male antifertility compounds from Tripterygium wilfordii Hook f.

Extracts of the Chinese medicinal plant, Tripterygium wilfordii, cause reversible infertility in male animals. Sub-fractionation studies have now revealed that the plant extracts contain a number of compounds which are potent antifertility agents in male mammals, including the diterpenes triptolide and tripdiolide and an isomer of the latter. A triptolide, 12,13-chlorohydrin, which is a transformation product formed reversibly by interaction of triptolide with HCl, was also found to be active.

Animals↗
PubMed1993

Induction of embryonic major histocompatibility complex antigen expression by gamma-IFN.

Preimplantation mouse embryos were incubated in vitro with mouse recombinant gamma-interferon (IFN). The effect of the gamma-IFN on major histocompatibility complex (MHC) class I antigen expression was tested using an ELISA procedure. It was found that there is a doubling of Db antigens and a tripling of Qa-2 antigens on C57BL/6 mouse embryos cultured from the 8-cell stage for 24 h in the presence of 10(5) units/ml gamma-IFN. The effect of gamma-IFN on the rate of preimplantation embryonic development was tested by culturing 2-cell embryos for 48 h and 8-cell embryos for 24 h in the presence of varying concentrations of gamma-IFN up to 10(6) units/ml. Two methods were used to assess the cell number per embryo after the culture period: incorporation of [3H]thymidine into DNA, and direct counting of nuclei in fixed and stained embryos. Both methods showed that treatment with gamma-IFN increases the rate of development of preimplantation mouse embryos. Since rate of preimplantation embryonic development is genetically controlled by the Ped gene, it is suggested that gamma-IFN has a direct effect on the Ped gene phenotype of preimplantation mouse embryos.

Animals↗
PubMed1993

Prevalence and aetiology of profound deafness in the general population of Sichuan, China.

People with profound deafness were surveyed in the general population of Sichuan. The results showed that the overall prevalence in Sichuan was 0.186 per cent (236/126,876) of the general population, males 0.212 per cent (135/63,741), females 0.159 per cent (101/63,135) (p < or = 0.05). Two hundred and fifteen (92 per cent) cases were older than 10 years, but 227 (96 per cent) lost their hearing under the age of 10 years, 192 (80 per cent) under five years, and 104 (44 per cent) were congenital. There was no significant difference in prevalence of deafness between the population located in urban and rural areas. However, the population living in the flat area and mountain area had a much higher prevalence than that of the hill people (p < or = 0.05). Amongst the nationalities investigated, there existed significant differences in prevalence. Both the population of the Hui and the Lisu presented a significantly higher prevalence of profound deafness than that of the others. In aetiology, genetic factors may account for 43 per cent (101/236) of the cases, amongst which, autosomal recessive (AR) deafness is 92 per cent (95/104) and autosomal dominant (AD) 5.4 per cent. Environmental factors were thought to be responsible for 35.6 per cent (84/236) of cases, including infectious diseases (31 per cent), ototoxic antibiotics (2.6 per cent), injury (1.7 per cent), and asphyxia (0.4 per cent). The number of cases of unknown origin were 20.3 per cent. It is suggested that, in China, the importance of genetic factors in hearing impairment should be emphasized. In addition, infectious diseases and ototoxicity play an important role in causing deafness.

Adolescent↗
PubMed1993

Outcome of pregnancy in diabetic ketoacidosis.

To evaluate the outcome of pregnancy in diabetic women who had an episode of ketoacidosis during gestation, 20 consecutive cases of ketoacidosis in type I diabetic pregnant women were studied. They were divided into two groups for comparison: Group 1, 13 patients (65%), had a live fetus and group 2, seven patients (35%), had a fetal death on admission. Both groups were similar in age, gravidity, parity, abortions, height, weight, serum sodium and potassium, arterial pH, carbon dioxide tension, bicarbonate, base excess, and anion gap. Significantly different between groups 1 and 2 were: gestational age (24 versus 31 weeks; p < 0.05), serum glucose (374 versus 830 mg/dl; p < 0.005), blood urea nitrogen (14 versus 23 mg/dl; p < 0.025), osmolality (295 versus 311 mmol/kg; p < 0.025), insulin requirements (127 versus 202 U; p < 0.05), and length of resolution (28 versus 38 hours; p < 0.05). Two patients had serum glucoses less than 200 mg/dl despite profound ketoacidosis. Precipitating factors included infections, poor compliance, and very importantly, unrecognized new onset of diabetes (6 patients). All stillborns were grossly normal and those autopsied had no discernible cause of death. There were no maternal deaths. A high fetal mortality (35%) was found but there were no fetal losses once therapy was initiated. The unrecognized new onset diabetics accounted for almost a third (30%) of the cases of ketoacidosis and for 57% of the fetal deaths. Attentiveness to the symptoms of uncontrolled diabetes and appropriate screening can be effective preventive measures.

Adult↗
PubMed1993

Modulation of preimplantation embryonic development by antisense oligonucleotides to major histocompatibility complex genes.

The Ped (preimplantation embryo development) gene, which controls the rate of mouse preimplantation embryonic cleavage division and subsequent survival of the embryo, maps to the Q region of the MHC (major histocompatibility complex). Mouse embryos were treated with antisense oligonucleotides to mRNA for the Q region genes Q7/Q9, each of which encodes the Qa-2 antigen. The reverse transcription polymerase chain reaction (RT-PCR) was used to show that antisense treatment, but not sense treatment, decreased the level of mRNA for Qa-2 antigen in preimplantation embryos. Furthermore, both the expression of Qa-2 protein and the rate of embryonic cleavage division were decreased by treatment with antisense but not sense oligonucleotides. These results provide direct evidence that the Ped gene phenotype is at least partially encoded by the Q7/Q9 genes. It is likely that the mouse Ped gene has a human homolog, perhaps within HLA-F. Identification of genes--such as the Ped gene--that affect survival of the embryo may be vitally important for the enhancement of animal and human reproductive success.

Animals↗
PubMed1993

Cytosolic triosephosphate isomerase is a single gene in rice.

A cDNA clone encoding rice (Oryza sativa L.) cytosolic triosephosphate isomerase (TPI), an important glycolytic enzyme, was isolated and characterized. The clone (pRTPI-6) contains an open reading frame of 759 base pairs, encoding a polypeptide chain of 253 amino acid residues (M(r) 27,060). The identity of this clone was defined by its high homology (85% nucleotide sequence and 89% amino acid sequence identical match) with a maize mRNA sequence encoding the cytosolic TPI and with TPIs from other species. Genomic DNA blot analysis using the cDNA as a probe showed that the cytosolic TPI gene is present as a single copy per haploid rice genome, as opposed to that found in maize, in which multiple TPI gene copies exist. A single TPI mRNA species of about 1100 nucleotides was detected by gel blot hybridization analysis of RNA isolated from root, culm, and leaf tissues, indicating that its expression is ubiquitous. Based on sequence comparison and molecular analysis, we propose that the chloroplast-located TPI may be encoded by divergent structural nuclear genes in rice.

Amino Acid Sequence↗