Search PubMed⌕ Search

Biomedical subjects

C Xu

Publications and source records attributed to C Xu.

At least 307 records · Page 17Linked to original sources
PubMed1993

Isolation of proteins associated with kinetoplast DNA networks in vivo.

Kinetoplast DNA (kDNA), the mitochondrial DNA of trypanosomes, is a highly condensed disc-shaped network of catenated DNA circles consisting of maxicircles, the equivalent of conventional mitochondrial DNA, and several thousand smaller circular DNAs termed minicircles. Upon cell lysis, kDNA expands, giving rise to a two-dimensional network of catenated circles with an overall diameter close to that of the whole cell. To identify proteins associated with the condensed form of kDNA in the cell, proteins were reversibly crosslinked to kDNA in whole cells of Crithidia fasciculata by formaldehyde treatment. Crosslinked networks were purified and found to retain a condensed structure which becomes fully expanded upon proteinase K treatment or reversal of the crosslinks by heating at 65 degrees C. Five low molecular weight proteins released from the kDNA by heat treatment were purified by polyacrylamide gel electrophoresis and their amino-terminal sequences were determined. PCR amplification and sequence analysis of cDNA sequences between these amino-terminal sequences and the miniexon (spliced leader) sequence present at the 5' end of all C. fasciculata mRNAs predicts the presence of 9-amino acid presequences with features characteristic of mitochondrial presequences on three of the proteins. Two of these proteins are lysine-rich basic proteins. These findings suggest that basic proteins may play a role in the condensation of kDNA in the kinetoplast and that these proteins are imported into the kinetoplast by a mechanism involving a cleavable presequence.

Amino Acid Sequence↗
PubMed1993

The effect of acidified glucose nutrient solution on preservation of platelet concentrate.

The preservation effect of a new platelet solution--acidified glucose nutrient solution (AGN)--was tested by adding AGN to pooled platelet rich plasma (PRP) prior to preparation of platelet concentrates (PC). Each PRP unit was prepared from a unit of whole blood and four PRP of the same blood group were pooled in 400 ml volume PVC bags. Equal aliquots of each pooled PRP were made prior to preparation of PC. AGN was added to one aliquot and nothing was added to the control aliquot. Equal volume and concentration PC were then prepared and the PC were further aliquoted for storage at 22 degrees C. After five days, the parameters of platelet count, pH, aggregability and hypotonic shock response (HSR) for PC preserved in AGN plasma were better than those of the controls preserved in normal ACD plasma. The aggregability and HSR of AGN platelet concentrates recovered to baseline after two h of incubation with fresh plasma. The results of electron microscopy show that platelets preserved in AGN have less changes in morphology. The results of our work suggest that the preservation effect of AGN on PC is similar to the effect of using second generation containers or preparation of platelets from thrombocytapheresis.

Blood Platelets↗
PubMed1993

A 300 bp 5'-upstream sequence of a differentiation-dependent rabbit K3 keratin gene can serve as a keratinocyte-specific promoter.

Keratinocytes of the suprabasal compartment of many stratified epithelia synthesize as a major differentiation product a keratin pair, consisting of an acidic and a basic keratin, which accounts for 10-20% of the newly synthesized proteins. While genes of several differentiation-related keratins have been cloned and studied, relatively little is known about the molecular basis underlying their tissue-specific and differentiation-dependent expression. We have chosen to study, as a prototype of these genes, the gene of K3 keratin, which has the unique property of being expressed in the majority of corneal epithelial basal cells but suprabasally in peripheral cornea, the site of corneal epithelial stem cells. Using a monoclonal antibody, AE5, specific for K3 keratin, and a fragment of human K3 gene as probes, we have isolated several cDNA and genomic clones of rabbit K3 keratin. One genomic clone has been sequenced and characterized, and the identity of its coding sequence with that of cDNAs indicates that it corresponds to the single, functional rabbit K3 gene. Transfection assays showed that its 3.6 kb 5'-upstream sequence can drive a chloramphenicol acetyl transferase (CAT) reporter gene to express in cultured corneal and esophageal epithelial cells, but not in mesothelial and kidney epithelial cells or fibroblasts, all of rabbit origin. Serial deletion experiments narrowed this keratinocyte-specific promoter to within -300 bp upstream of the transcription initiation site. Its activity is not regulated by the coding or 3'-noncoding sequences that have been tested so far. This 300 bp 5'-upstream sequence of K3 keratin gene, which can function in vitro as a keratinocyte-specific promoter, contains two clusters of partially overlapping motifs, one with an NFkB consensus sequence and another with a GC box. The combinatorial effects of these multiple motifs and their cognate binding proteins may play an important role in regulating the expression of this tissue-restricted and differentiation-dependent keratin gene.

Amino Acid Sequence↗
PubMed1993

Modeling of the last stage of production phase of oxytetracycline fermentation processes.

In an attempt to disclose the reason why, during the last stage of FBOFP (fed-batch oxytetracycline fermentation processes) its specific production rate in general decreases notably, the authors started with the modeling of the process based on operation data, and thus reached the conclusion that this is due to too low residual nitrogen in the substrate. This inference is quite unacceptable to the current practice of the process operations. It was finally realized that the trouble lies in that our old measurement method of residual nitrogen is misleading. Upon using improved measuring method, it was found that while the total residual nitrogen is plentiful, the available nitrogen notably decreases with time, and thus confirmed the authors' conclusions. Experiments on industrial fermentators showed that the product can be increased by 1%, and the titer reaches 3200 micrograms/ml.

Fermentation↗
PubMed1993

[Study on determination of polyactin A by ELISA].

Sandwich ELISA and two-step competition ELISA were utilized to determine polyactin A. After optimization of the experimental conditions, microtiter plates were coated with the rabbit antibody solution and evaporated to dryness at 37 degrees C. The coated microtiter plates were incubated first with the analyte, then with the HRP-labelled antibody (sandwich procedures), or with the HRP-labelled polyactin A (competition procedures), and absorbance was measured after coloration. The whole determination took less than 4 hours, excluding the coating procedure, which is faster than the routine complement fixation method. The coated microtiter plates can be well after over three months of storage at 4 degrees C. The sensitivity obtained was 0.64-7.4 ng/well for the sandwich method or 0.6-1.2 micrograms/well for the competition method.

Adjuvants, Immunologic↗
PubMed1992

Similarity between the Myxococcus xanthus and Stigmatella aurantiaca reverse transcriptase genes associated with multicopy, single-stranded DNA.

To determine the evolutional relationship of bacterial retroelements of Myxococcus xanthus and Stigmatella aurantiaca, the nucleotide sequence of 3,060 bases encompassing msr, msd, and the upstream region of msd (downstream of msr) of S. aurantiaca DW4 was determined and compared with the same region from M. xanthus. An open reading frame was found 92 bases upstream of msd which encoded a polypeptide of 480 amino acid residues having 73% identity with the reverse transcriptase of M. xanthus. Together with high homologies in msr (86%) and msd (81%) regions, the present data indicate that the reverse transcriptase genes as well as the retrons of M. xanthus (retron-Mx162) and S. aurantiaca (retron-Sa163) were derived from a common progenitor retron which possibly before the two myxobacterial species diverged.

Amino Acid Sequence↗
PubMed1992

[Preparation of sucking tablet of shengmei] off.

The Sucking Tablet of Shengmei is made from eight Chinese traditional drugs including Radix Adenophorae, Fructus Mume, etc. The effective rate of the tablet in treating chronic pharyngitis reaches up to 96 percent. The working mechanism related to the fact that the tablet is bacteria-resistant and helps to strengthen the body function. This paper presents the preparation process of the Sucking Tablet along with solutions for some problems encountered in the process and appropriate standards for quality control.

Animals↗
PubMed1991

Activated macrophages in highly irradiated cercariae-induced immunity to Schistosoma japonicum in rats.

The results of studies on the schistosomulicidal activity of activated peritoneal and alveolar macrophages (pM phi and aM phi) from rats immunized with highly irradiated (50 krad.) Schistosoma japonicum cercariae are reported. The authors have examined the activation of these macrophages in terms of spreading, adhesion and ingestion of sheep erythrocytes and pinocytosis of horse-radish peroxidase. Using three criteria, peritoneal macrophages and alveolar macrophages from immunized rats and from rats intraperitoneally injected with BCG were significantly more active than those from normal rats or rats stimulated with 10% proteose-peptone or 1% sodium thioglycolate. A significantly higher percentage of adhesion and ingestion was obtained with the sheep erythrocytes that were co-opsonized by heat-inactivated rat anti-sheep erythrocyte serum and fresh normal rat serum. Schistosomulicidal effects were observed with macrophages from irradiated cercariae-immunized rats in two activation systems: in vitro activation in the presence of macrophage-activating factor (MAF), and in vivo activation by the intraperitoneal challenge with sonicated cercarial antigens.

Animals↗
PubMed1991

Ventilatory response of the sleeping newborn to CO2 during normoxic rebreathing.

The ventilatory response of the newborn to CO2 was studied using a rebreathing method that minimized changes in arterial PO2 during the test. The aim was to study the variability of the ventilatory response to CO2 and take this into account to assess the relative magnitude of the response to CO2 during rapid-eye-movement (REM) sleep and quiet sleep (QS). Five full-term babies aged 4-6 days were given 5% CO2 in air to rebreathe for 1.5-3 min. O2 was added to the rebreathing circuit to maintain arterial O2 saturation and transcutaneous PO2 (Ptco2) at prerebreathing levels. Tests were repeated four to five times in REM sleep and QS. Mean Ptco2 levels varied between individuals but were similar during REM sleep and QS tests for each subject. The mean coefficient of variability of the ventilatory response was 35% (range 15-77%) during QS and 120% (range 32-220%) during REM sleep. PtcO2 fluctuations during tests [6.0 +/- 3.0 (SD) Torr, range 1-13 Torr] were not correlated with ventilatory response. Overall the ventilatory response was significantly lower in REM sleep than in QS (12.2 +/- 3.0 vs. 38.7 +/- 3.0 ml.min-1.Torr-1.kg-1, P less than 0.001; 2-way analysis of variance) due to a small (nonsignificant) fall in the tidal volume response and a significant fall in breathing rate. In 12 REM sleep tests there was no significant ventilatory response; mean inspiratory flow increased significantly during 8 of these 12 tests. We conclude that there is a significant decrease in the ventilatory response of the newborn to CO2 rebreathing during REM sleep compared with QS.

Carbon Dioxide↗
PubMed1991

[Effects of verticillatine on cerebral blood flow, cerebral vascular resistance and blood pressure in anesthetized dogs and cats].

The effects of verticillatine (Ver), hexamethonium (Hex) and nimodipine (Nim) on mean arterial pressure (MAP), cerebral blood flow (CBF) and cerebrovascular resistance (CVR) were determined in pentobarbital anesthetized animals using the method of electromagnetic flow meter in dogs and hydrogen clearance in cats. Ver or Nim iv induced significant reduction of MAP and CVR. CBF was increased in dogs and unaltered in cats. The Hex treated dogs and cats exhibited a fall of MAP and CBF with enhancement of CVR. In cats after middle cerebral artery occlusion (MCAO), regional cerebral blood flow (rCBF) was reduced from 190 +/- 70 to 90 +/- 20 ml.kg-1.min-1. Ver and Nim iv caused similar changes of MAP and CVR to those before MCAO. The results suggest that Ver and Nim may have vasodilation effect and improve the cerebral circulation. Thus, they would be beneficial to patients suffering from hypertension.

Animals↗
PubMed1991

[A study on autoimmune response against spermatozoa following intravas deferens injection of high molecular hydrogel HFMC in rabbits].

To investigate whether intravas injection of HFMC can result in antisperm antibodies, we divided 30 fertile male rabbits into the DMSO, 10% HFMC and 20% HFMC groups. Two to 8 months after intravas injection of the agents, we collected the sera per month and used ELISA to detect the serum antisperm antibodies, The results showed that there are lower antisperm antibody levels in the sera of DMSO, 10% HEMC and 20% HFMC groups in the first 2 months (P less than 0.05), but no significant difference between the antibody levels of DMSO, 10% and 20% HFMC groups and that of the control group from the 3rd month to the 8th month (P greater than 0.05). No immune-related pathological changes were found in the testis and epididymis. Intravas injection of HFMC in the rabbits appears to be a safe method of contraception that causes no deleterious effects.

Animals↗
PubMed1991

[Separation and identification of main medicinal saponin components from mass cell cultures of Panax notoginseng (Burk) F. H. Chen].

Five main saponins were separated from the cell cultures of Panax notoginseng (Burk) F. H. Chen. They were sanchinoside Rb1, Re, R1, Rg1 and Rh1 identified by TLC, HPLC, IR, M. P., 13CNMR and EI-MS. Saponin components of the cell cultures were almost the same as those of the cultivated plants. But the content of saponins was different between the cell cultures and the cultivated plants. Saponin extraction and separation procedure suitable for the cell cultures has to be different from that for the cultivated plants.

Medicine, Chinese Traditional↗