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C Guan

Publications and source records attributed to C Guan.

At least 37 records · Page 2Linked to original sources
PubMed1999

[Evaluation of N staging of cervical lymph nodes with positive palpation in laryngeal carcinoma].

OBJECTIVE: To evaluate N staging of cervical lymph nodes with positive palpation objectively. METHOD: Serial sections of lymph nodes of neck dissections with transparent methods were observed under light microscope. RESULT: 81 lymph nodes with pathological metastases were verified in 100 patients with 114 palpation positive lymph nodes. The correspondent rate was 71.1%. The correspondent rate of clinical N via pathological N staging was N1 35.6%, N2a 25.0%, N2b 58.3%, N2c 75.0%, N3 100.0% respectively. CONCLUSION: N staging judged only by palpation is not sufficient in clinic. It should be combined with other examinations.

Carcinoma, Squamous Cell↗
PubMed1999

[Pathologic feature of occult lymphatic metastasis in supraglottic carcinoma].

OBJECTIVE: To study the pathologic features of occult lymphatic metastasis in patients with supraglottic carcinoma and its implication in treatment. METHODS: Serial sections of 153 neck dissection specimens in 100 patients with supraglottic carcinoma were studied under microscope. RESULTS: Clinically negative nodes had been proved histologically positive in 58 specimens (38%) and 51 occult nodes, size ranged from 0.5 cm to 2.6 cm with average of 1.1 cm. The distribution of metastastic lymph nodes was 1 in level I (2%), 37 in level II (73%), 12 in level III(23%) and 1 in level IV(2%). Among the 51 nodes, 21(41%) were in early stage, 18 (35%) in growth stage, 7(14%) in full stage, 5(10%) were extracapsular. CONCLUSION: Occult metastasis rate of supraglottic carcinoma is as high as 38%, selective neck dissection is recommended for the surgical treatment of this disease.

Adult↗
PubMed1998

Regulation of polar auxin transport by AtPIN1 in Arabidopsis vascular tissue.

Polar auxin transport controls multiple developmental processes in plants, including the formation of vascular tissue. Mutations affecting the PIN-FORMED (PIN1) gene diminish polar auxin transport in Arabidopsis thaliana inflorescence axes. The AtPIN1gene was found to encode a 67-kilodalton protein with similarity to bacterial and eukaryotic carrier proteins, and the AtPIN1 protein was detected at the basal end of auxin transport-competent cells in vascular tissue. AtPIN1 may act as a transmembrane component of the auxin efflux carrier.

Amino Acid Sequence↗
PubMed1998

AtPIN2 defines a locus of Arabidopsis for root gravitropism control.

The molecular mechanisms underlying gravity perception and signal transduction which control asymmetric plant growth responses are as yet unknown, but are likely to depend on the directional flux of the plant hormone auxin. We have isolated an Arabidopsis mutant of the AtPIN2 gene using transposon mutagenesis. Roots of the Atpin2::En701 null-mutant were agravitropic and showed altered auxin sensitivity, a phenotype characteristic of the agravitropic wav6-52 mutant. The AtPIN2 gene was mapped to chromosome 5 (115.3 cM) corresponding to the WAV6 locus and subsequent genetic analysis indicated that wav6-52 and Atpin2::En701 were allelic. The AtPIN2 gene consists of nine exons defining an open reading frame of 1944 bp which encodes a 69 kDa protein with 10 putative transmembrane domains interrupted by a central hydrophilic loop. The topology of AtPIN2p was found to be similar to members of the major facilitator superfamily of transport proteins. We have shown that the AtPIN2 gene was expressed in root tips. The AtPIN2 protein was localized in membranes of root cortical and epidermal cells in the meristematic and elongation zones revealing a polar localization. These results suggest that AtPIN2 plays an important role in control of gravitropism regulating the redistribution of auxin from the stele towards the elongation zone of roots.

Amino Acid Sequence↗
PubMed1998

Crystal structures of Flavobacterium glycosylasparaginase. An N-terminal nucleophile hydrolase activated by intramolecular proteolysis.

Glycosylasparaginase (GA) is a member of a novel family of N-terminal nucleophile hydrolases that catalytically use an N-terminal residue as both a polarizing base and a nucleophile. These enzymes are activated from a single chain precursor by intramolecular autoproteolysis to yield the N-terminal nucleophile. A deficiency of GA results in the human genetic disorder known as aspartylglycosaminuria. In this study, we report the crystal structure of recombinant GA from Flavobacterium meningosepticum. Similar to the human structure, the bacterial GA forms an alphabetabetaalpha sandwich. However, some significant differences are observed between the Flavobacterium and human structures. The active site of Flavobacterium glycosylasparaginase is in an open conformation when compared with the human structure. We also describe the structure of a mutant wherein the N-terminal nucleophile Thr152 is substituted by a cysteine. In the bacterial GA crystals, we observe a heterotetrameric structure similar to that found in the human structure, as well as that observed in solution for eukaryotic glycosylasparaginases. The results confirm the suitability of the bacterial enzyme as a model to study the consequences of mutations in aspartylglycosaminuria patients. They also suggest that further studies are necessary to understand the detail mechanism of this enzyme. The presence of the heterotetrameric structure in the crystals is significant because dimerization of precursors has been suggested in the human enzyme to be a prerequisite to trigger autoproteolysis.

Amino Acid Sequence↗
PubMed1998

Site-directed mutagenesis of essential residues involved in the mechanism of bacterial glycosylasparaginase.

Flavobacterium glycosylasparaginase was cloned in an Escherichia coli expression system. Site-directed mutagenesis was performed at residues suggested to be important in the catalytic mechanism based on the crystal structure of the human enzyme and other biochemical studies. In vitro autoproteolysis allowed the mutant enzymes to be activated, including those that were slow to self-cleave. Based on the activity of the mutant enzymes, six catalytically essential amino acids were identified: Trp-11, Asp-66, Thr-152, Thr-170, Arg-180, and Asp-183. Kinetic analysis of each mutant further defined the function of these residues in substrate specificity and reaction rate. Mutagenesis of the N-terminal nucleophile residue Thr-152 confirmed the key function of its side-chain hydroxyl group. Partial activities of mutants T152S/C were in agreement with the general mechanism of N-terminal nucleophile (Ntn)-amidohydrolases. The side-chain hydroxyl of Thr-170 contributes to the reaction rate based on studies of mutants T170S/C/A. Residues Asp-183 and Arg-180 were found to H-bond, respectively, with the charged alpha-amino and alpha-carboxyl group of the substrate (Asn-GlcNAc). Mutants R180Q/L and D183E/N had greatly decreased substrate affinity and reduced reaction rates. Kinetic studies also showed that Trp-11 is involved in regulation of the enzyme reaction rate, contradictory to a previous suggestion that this residue is involved in substrate binding. Asp-66 is a new residue found to be important in enzyme activity. The overall active site structure involving these catalytic residues resembles the glutaminase domain of glucosamine 6-phosphate synthase, another member of the Ntn-amidohydrolase family of enzymes.

Amino Acid Substitution↗
PubMed1998

Characterization and functional analysis of the cis-autoproteolysis active center of glycosylasparaginase.

Glycosylasparaginase is an N-terminal nucleophile hydrolase and is activated by intramolecular autoproteolytic processing. This cis-autoproteolysis possesses unique kinetics characterized by a reversible N-O acyl rearrangement step in the processing. Arg-180 and Asp-183, involved in binding of the substrate in the mature enzyme, are also involved in binding of free amino acids in the partially formed substrate pocket on certain mutant precursors. This binding site is sequestered in the wild-type precursor. Binding of free amino acids on mutant precursors can either inhibit or accelerate their processing, depending on the individual mutants and amino acids. The polypeptide sequence at the processing site, which is highly conserved, adopts a special conformation. Asp-151 is essential for maintaining this conformation, possibly by anchoring its side chain into the partially formed substrate pocket through interaction with Arg-180. The reactive nucleophile Thr-152 is activated not only by deprotonation by His-150 but also by interaction with Thr-170, suggesting a His-Thr-Thr active triad for the autoproteolysis.

ATP-Binding Cassette Transporters↗
PubMed1998

Crystal structure of glycosylasparaginase from Flavobacterium meningosepticum.

The crystal structure of recombinant glycosylasparaginase from Flavobacterium meningosepticum has been determined at 2.32 angstroms resolution. This enzyme is a glycoamidase that cleaves the link between the asparagine and the N-acetylglucosamine of N-linked oligosaccharides and plays a major role in the degradation of glycoproteins. The three-dimensional structure of the bacterial enzyme is very similar to that of the human enzyme, although it lacks the four disulfide bridges found in the human enzyme. The main difference is the absence of a small random coil domain at the end of the alpha-chain that forms part of the substrate binding cleft and that has a role in the stabilization of the tetramer of the human enzyme. The bacterial glycosylasparaginase is observed as an (alphabeta)2-tetramer in the crystal, despite being a dimer in solution. The study of the structure of the bacterial enzyme allows further evaluation of the effects of disease-causing mutations in the human enzyme and confirms the suitability of the bacterial enzyme as a model for functional analysis.

Aspartylglucosylaminase↗
PubMed1998

[Significance of pathological type in cervical lymph metastasis of laryngeal cancer].

To research significance of pathological type in cervical lymph metastasis of laryngeal cancer. Observing metastasis lymph nodes in serial sections of 55 cases neck dissection specimens with microscope. Single type 21 cases, 90% of them were occult metastasis, three-year survival rate was 90%. Multiple types 10 cases, 70% of them were occult metastasis, three-year survival rate was 70%. Gathering type 24 cases, 92% of them can be palpated by physician, three-year survival rate was 54%. It is suitable that cervical metastasis lymph nodes of laryngeal cancer were divided into three types in pathology. It is significance for treatment and prognosis.

Adult↗
PubMed1997

Cloning and biochemical characterization of an anionic peroxidase from Zea mays.

We have isolated, cloned and characterized a cDNA from Zea mays L., denoted ZmAP1, coding for an anionic peroxidase. The open reading frame of ZmAP1 starting 72 residues from the 5' end of the cDNA predicts a 37,778 dalton protein of 356 amino acid residues. The protein has high similarity to other peroxidases and contains two peroxidase motifs that carry two highly conserved histidines in the active center. We expressed recombinant ZmAP1 protein in E. coli as a fusion with maltose-binding protein. The fusion protein was biochemically active after addition of hemin to the apoprotein. The maize peroxidase ZmAP1 has a pH optimum at pH 4.0 and a Km of 0.2 mM for the substrate 2,2'-azino-bis-(3-ethyl-benzothiazolin-6-sulfonic acid) at this pH. In maize seedlings the ZmAP1 gene is expressed predominantly in roots, the mesocotyl, the coleoptile and to a lower extent in the node, whereas no expression in the primary leaf was found. In situ hybridization shows that the expression of ZmAP1 in the young maize root is confined to the epidermis, hypodermis and the pericycle.

Amino Acid Sequence↗
PubMed1997

A nodule-specific gene family from Alnus glutinosa encodes glycine- and histidine-rich proteins expressed in the early stages of actinorhizal nodule development.

Two cDNAs representing different members (agNt84 and ag164) of a gene family encoding glycine- and histidine-rich proteins have been isolated from cDNA libraries from Alnus glutinosa root nodules. Expression of the corresponding genes could only be detected in nodules. With in situ hybridization, the expression in nodules was found to occur in young, infected cells of the prefixation zone (zone 2). The encoded proteins contain putative signal peptides for targeting to the endomembrane system, sharing sequence similarity with signal peptides from plant glycine-rich proteins, among them nodulin 24, a nodule-specific protein from soybean. This similarity suggests that, analogous to nodulin-24, proteins encoded by agNt84/ag164 may be located at the interface between the host plant membrane and the matrix surrounding the endosymbiont. The 3' untranslated regions of the cDNAs contain unusual poly(AT)n stretches that may play a role in the regulation of RNA stability. The protein encoded by agNt84 cDNA was expressed in Escherichia coli as a fusion with maltose-binding protein, and was shown to have the ability to bind to a nickel-chelating resin, indicating that it may function as a metal-binding protein.

Actinomycetales↗
PubMed1997

[Clinical and pathological study on cervical lymph node metastasis of supraglottic cancer].

AIM: To study pathological features of cervical lymph node metastasis and the relationship between supraglottic cancer and cervical lymph node metastasis. METHOD: Observation of 100 whole-organ serial sections of the larynges and 170 sides of the radical neck dissection specimens. RESULTS: 1. Cervical lymph node metastasis 55 cases, metastatic rate 55%; 2. Four series of cervical metastasis: clinico-pathologic metastases (29 cases), pathologic metastases (26 cases), clinical metastases (5 cases), no metastasis (40 cases). 3. Four stages of metastatic lymphnode: early stage, growth stage, fullness stage and capsular perforative stage; 4. Three types of metastases: single type (21 cases), multiple type (10 cases) and aggregated (24 cases) type. 5. Metastatic rates of supraglottic cancer of different regions: aryepiglottic fold 85.7%, arytenoid cartilage area 66.6%, epiglotto-ventricular fold 56.8%, epiglottic 46.4%, ventricular fold 45.4%. 6. When the tumour spread to the perilaryngeal region, the metastatic rate was 80% to 84%. CONCLUSION: Metastatic rate of cervical lymph node is higher in supraglottic cancers, the aggregated type and capsular perforative stage are more in metastasis lymph nodes. Analysis the original sites of supraglottic cancer is conductive to the prediction of the cervical lymph node metastasis.

Glottis↗
PubMed1996

Activation of glycosylasparaginase. Formation of active N-terminal threonine by intramolecular autoproteolysis.

The activation mechanism of glycosylasparaginase of Flavobacterium meningosepticum has been analyzed by site-directed mutagenesis and activation of purified precursors in vitro. Mutation of Thr-152 to Ser or Cys leads to gene products that are not activated in vivo but are activated in vitro because processing of the mutant precursors is inhibited by certain amino acids in the cell. Kinetic studies reveal that activation is an intramolecular autoproteolytic process. The involvement of His-150 and Thr/Ser/Cys-152 in activation suggests that autoproteolysis resembles proteolysis by serine/cysteine proteases. Multiple functions of the highly conserved active threonine residue are implicated.

Amino Acid Sequence↗
PubMed1996

Nitrogen metabolism in actinorhizal nodules of Alnus glutinosa: expression of glutamine synthetase and acetylornithine transaminase.

Two nodule cDNA clones representing genes involved in Alnus glutinosa nitrogen metabolism were analysed. ag11 encoded glutamine synthetase (GS), the enzyme responsible for ammonium assimilation, while ag118 encoded acetylornithine transaminase (AOTA), an enzyme involved in the biosynthesis of citrulline, the nitrogen transport form in Alnus. GS mRNA was found at highest levels in root nodules, where it was present in the infected cells as well as in the cells of the pericycle of the vascular system. AOTA transcripts were found at high levels in nodules, confined to the infected cells, suggesting that in nodules of A. glutinosa, citrulline biosynthesis takes place mainly in the infected cells.

Actinomycetales↗
PubMed1996

[The preparation of hepatic receptor imaging agent 99mTc-DTPA-NGA].

The method of preparation and the character of the hepatic receptor imaging agent 99mTc-DTPA-NGA have been presented. The radio-chemical purity of the imaging agent is higher than 95% and the stability of the imaging agent is more than 6 hours in vitro and in human blood. The agent is able to tend to liver and has the character of receptor-intervene-conduct binding. Our comparative study of 99mTc-DTPA-NGA versus 99mTc-NGA reveals, the stability of the former in vitro and in human blood is better than that of the latter. The imaging in rabbits shows that the imaging quality of the former is higher than that of the latter. The radioactive metabolites in urine have been examined. The former does not fall off 99mTc in vivo, but the latter falls off 99mTc clearly. 10 clinical hepatic imagings have had satisfactory results.

Albumins↗
PubMed1996

[Preparation of galactosyl-cytochrome C and studies on its hepatic targeting property].

This paper reports the preparation of the coupling compound between thiogalactose and cytochrome C(Cyt-C). The binding tests of this compound to asialoglycoprotein receptor have also been carried out in vivo. The results show that the pharmacokinetics of this compound is in accordance with the basic characteristic of receptor induced binding. The highest uptake of liver reaches to 32.9% and at the same time the conjugate remains 78.6% the biological activity of Cyt-C. It is possibly a hepatic targeting drug or a hepatic targeting carrier.

Animals↗
PubMed1996

[A study of the relevant factors of removal of common bile duct stones with endoscopic mechanical lithotripsy].

Endoscopic mechanical lithotripsy (EML) was attempted in 41 patients with common bile duct stones unable to be removed by endoscopic sphincterotomy. These patients had altogether 89 stones with stone size ranged from 5 to 30 mm (mean transverse diameter 16.6 +/- 6.0 mm and mean longitudinal diameter 20.0 +/- 7.1 mm). 31 patients had 34 stones greater than or equal to 20 mm in transverse diameter. The overall stone removal rate was 97.6%. The rate of complete removal of the stone fragments with EML at one time was 78.6% (11/14) for large, 58.8% (10/17) for middle and 0 (0/5) for small incision of the sphincter. In patients with diameter of the distal common bile duct greater than or equal to 14 mm and less than 9 mm the rate was 83.3% and 30.8% respectively and the difference was of significance (P < 0.05). The rate of complete removal for using basket and balloon catheter was 6/10 and 4/9 separately and that for combined used of these two methods 83.3% (10/12). The rate of spontaneous passage of the stone (within one week) was 1/5. It is concluded that complete removal of the stone fragments was related mainly to the length of the incision, diameter of distal common bile duct and methods of removing stone fragments after the crush with lithotripsy basket; when the stone is large and there is the no space around the stone for lithotripsy basket manipulation, a large amount of diluted contrast material is injected into the bile duct so as to increase the space and facilitate the ensonaring of the stone with lithotripsy basket. Hard stones can not be crushed easily, so they constitute one of the reasons of failure.

Adult↗