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Biomedical subjects

N Li

Publications and source records attributed to N Li.

At least 379 records · Page 21Linked to original sources
PubMed1993

[Measurement of the single muscle fiber action potentials and jitter value in tibialis anterior muscles of rabbits in situ].

With a home-made jitter data processing board and microcomputer for recording extracellular single fiber action potential (SF-AP), variations of the time intervals of the SF-AP pairs, or the jitters, from two adjacent muscle fibers in the unique motor unit in tibialis' anterior in response to repeated stimuli were measured. The jitter distribution of 936 recorded from 7 rabbits was positively showed with a percentile value of P75-P25 of 54.99-14.61 microseconds. The data suggested that the lower limit was smaller than that of skeletal muscles in normal human and that there exists also some differences in the jitter values of SFEMG between human and rabbit muscles.

Action Potentials↗
PubMed1992

Point mutation in FGF receptor eliminates phosphatidylinositol hydrolysis without affecting mitogenesis.

Stimulation of growth factor receptors with tyrosine kinase activity is followed by rapid receptor dimerization, tyrosine autophosphorylation and phosphorylation of signalling molecules such as phospholipase C gamma (PLC gamma) and the ras GTPase-activating protein. PLC gamma and GTPase-activating protein bind to specific tyrosine-phosphorylated regions in growth factor receptors through their src-homologous SH2 domains. Growth factor-induced tyrosine phosphorylation of PLC gamma is essential for stimulation of phosphatidylinositol hydrolysis in vitro and in vivo. We have shown that a short phosphorylated peptide containing tyrosine at position 766 from a conserved region of the fibroblast growth factor (FGF) receptor is a binding site for the SH2 domain of PLC gamma (ref. 8). Here we show that an FGF receptor point mutant in which Tyr 766 is replaced by a phenylalanine residue (Y766F) is unable to associate with and tyrosine-phosphorylate PLC gamma or to stimulate hydrolysis of phosphatidylinositol. Nevertheless, the Y766F FGF receptor mutant can be autophosphorylated, and can phosphorylate several cellular proteins and stimulate DNA synthesis. Our data show that phosphorylation of the conserved Tyr 766 of the FGF receptor is essential for phosphorylation of PLC gamma and for hydrolysis of phosphatidylinositol, but that elimination of this hydrolysis does not affect FGF-induced mitogenesis.

Animals↗
PubMed1992

A functional tomato ACC synthase expressed in Escherichia coli demonstrates suicidal inactivation by its substrate S-adenosylmethionine.

1-Aminocyclopropane-1-carboxylate (ACC) synthase is a key enzyme in the biosynthesis of the plant hormone, ethylene. We have isolated, sequenced and expressed a functional tomato (cv Pik-Red) ACC synthase gene in Escherichia coli. ACC synthase expressed in E. coli was inactivated by incubation with S-adenosylmethionine (SAM), the half-time of which was concentration dependent. Mixing the tomato fruit protein extract with the cell-free extract from transformed E. coli did not affect SAM-dependent inactivation of ACC synthase activity. Thus, single isoforms of the ACC synthase enzyme, which demonstrate the biochemical features expected of the tomato fruit enzyme, can be expressed in E. coli and their structure-function relationships investigated.

Amino Acid Sequence↗
PubMed1992

Comparative efficacy of alternative hand-washing agents in reducing nosocomial infections in intensive care units.

BACKGROUND: Effective hand-washing can prevent nosocomial infections, particularly in high-risk areas of the hospital. There are few clinical studies of the efficacy of specific hand-cleansing agents in preventing the transmission of pathogens from health care workers to patients. METHODS: For eight months, we conducted a prospective multiple-crossover trial involving 1894 adult patients in three intensive care units (ICUs). In a given month, the ICU used a hand-washing system involving either chlorhexidine, a broad-spectrum antimicrobial agent, or 60 percent isopropyl alcohol with the optional use of a nonmedicated soap; in alternate months the other system was used. Rates of nosocomial infection and hand-washing compliance were monitored prospectively. RESULTS: When chlorhexidine was used, there were 152 nosocomial infections, as compared with 202 when the combination of alcohol and soap was used (adjusted incidence-density ratio [IDR], 0.73; 95 percent confidence interval, 0.59 to 0.90). The largest reduction with chlorhexidine was in gastrointestinal infections (IDR, 0.19; 95 percent confidence interval, 0.05 to 0.64). When chlorhexidine was available, the rates of nosocomial infection declined in each of the ICUs, and health care workers washed their hands more often than when alcohol and soap were used (relative risk, 1.28; 95 percent confidence interval, 1.02 to 1.60). The total volume of alcohol and soap used was 46 percent that of chlorhexidine (P less than 0.001). CONCLUSIONS: A hand-disinfection system using an antimicrobial agent (chlorhexidine) reduces the rate of nosocomial infections more effectively than one using alcohol and soap. The improvement may be explained at least in part by better compliance with hand-washing instructions when chlorhexidine was used.

1-Propanol↗
PubMed1992

Electrocardiographic abnormalities and associated factors in Chinese living in Beijing and in Mauritius. The Mauritius Non-Communicable Disease Study Group.

OBJECTIVE: To compare the prevalence of electrocardiographic abnormalities and to evaluate the association between these abnormalities and the levels of coronary heart disease among Chinese living in different environments. DESIGN: Cross sectional surveys. SETTING: Beijing, China, and the island of Mauritius. SUBJECTS: Random samples of people aged 35-64 years in Beijing (621 men, 642 women) in 1984 and in Mauritius among Chinese (137 men, 130 women) and non-Chinese (1265 men, 1432 women) in 1987. MAIN OUTCOME MEASURES: Prevalence of electrocardiographic abnormalities suggesting coronary heart disease and of associated risk factors. RESULTS: Prevalence of electrocardiographic abnormalities suggesting coronary heart disease was significantly lower in Beijing (4.0%) than in Mauritian Chinese (24.3%) and Mauritian non-Chinese (24.5%). Mean serum concentrations of total and non-high density lipoprotein cholesterol were lower in Beijing Chinese than in Mauritian Chinese, but smoking and hypertension were slightly more prevalent. Overall, men with electrocardiographic abnormalities had higher risk factor levels than those with a normal electrocardiogram regardless of ethnic origin. CONCLUSIONS: The prevalence of coronary heart disease and associated risk factors was different among Chinese living in two different environments: in Beijing in the People's Republic of China and in Mauritius. Chinese, who traditionally have a very low frequency of coronary heart disease, are by no means protected against coronary heart disease and other non-communicable diseases. Therefore, primary prevention of coronary heart disease is a major challenge for preventive medicine in China, as well as in many other developing countries.

Adult↗
PubMed1992

Site-directed conversion of a cysteine to aspartate leads to the assembly of a [3Fe-4S] cluster in PsaC of photosystem I. The photoreduction of FA is independent of FB.

The terminal electron acceptors FA and FB exist as two [4Fe-4S] clusters located on the 8.9-kDa PsaC protein in photosystem I. We have used site-directed mutagenesis to produce a complementary pair of mutant PsaC proteins in which specific cysteine ligands to the [4Fe-4S] clusters were changed to aspartic acid residues. The mutant proteins, denoted C14D and C51D, were overproduced in Escherichia coli; the iron-sulfur clusters were inserted in vitro; and the reconstituted proteins were rebound to the P700-FX core of Synechococcus sp. PCC 6301 in the presence of the PsaD protein. In complexes reconstituted with C51D a rhombic ESR spectrum with g-values of 2.063, 1.934, and 1.879 in the reduced state identifies the intact [4Fe-4S] cluster as FB, while an intense axial spectrum with g-values of 2.020 and 1.997 in the oxidized state identifies the altered cluster in the aspartate site as a [3Fe-4S] cluster. The [3Fe-4S] cluster corresponding to FA can be reduced chemically with dithionite and photochemically by illumination at room temperature but is not reduced by illumination at 15 K. With reconstituted C14D a rhombic ESR spectrum with g-values of 2.043, 1.942, and 1.853 in the reduced state identified the unaltered [4Fe-4S] cluster as FA, while a complex spectrum with a gz-value of 2.194 and an asymmetric gx,y set of resonances between 2.092 and 1.999 indicates an altered cluster of unknown identity in the site containing the aspartate ligand. The ESR signals arising from the altered cluster corresponding to FB are not diminished by illumination at either room temperature or 15 K.(ABSTRACT TRUNCATED AT 250 WORDS)

Aspartic Acid↗
PubMed1992

SH2 domains prevent tyrosine dephosphorylation of the EGF receptor: identification of Tyr992 as the high-affinity binding site for SH2 domains of phospholipase C gamma.

Several cytoplasmic tyrosine kinases contain a conserved, non-catalytic stretch of approximately 100 amino acids called the src homology 2 (SH2) domain, and a region of approximately 50 amino acids called the SH3 domain. SH2/SH3 domains are also found in several other proteins, including phospholipase C-gamma (PLC gamma). Recent studies indicate that SH2 domains promote association between autophosphorylated growth factor receptors such as the epidermal growth factor (EGF) receptor and signal transducing molecules such as PLC gamma. Because SH2 domains bind specifically to protein sequences containing phosphotyrosine, we examined their capacity to prevent tyrosine dephosphorylation of the EGF and other receptors with tyrosine kinase activity. For this purpose, various SH2/SH3 constructs of PLC gamma were expressed in Escherichia coli as glutathione-S-transferase fusion proteins. Our results show that purified SH2 domains of PLC gamma are able to prevent tyrosine dephosphorylation of the EGF receptor and other receptors with tyrosine activity. The inhibition of tyrosine dephosphorylation paralleled the capacity of various SH2-containing constructs to bind to the EGF receptor, suggesting that the tyrosine phosphatase and the SH2 domain compete for the same tyrosine phosphorylation sites in the carboxy-terminal tail of the EGF receptor. Analysis of the phosphorylation sites protected from dephosphorylation by PLC gamma-SH2 revealed substantial inhibition of dephosphorylation of Tyr992 at 1 microM SH2. This indicates that Tyr992 and its flanking sequence is the high-affinity binding site for SH2 domains of PLC gamma.(ABSTRACT TRUNCATED AT 250 WORDS)

3T3 Cells↗
PubMed1992

Accumulation of wound-inducible ACC synthase transcript in tomato fruit is inhibited by salicylic acid and polyamines.

Regulation of wound-inducible 1-aminocyclopropane-1-carboxylic acid (ACC) synthase expression was studied in tomato fruit (Lycopersicon esculentum cv. Pik-Red). A 70 base oligonucleotide probe homologous to published ACC synthase cDNA sequences was successfully used to identify and analyze regulation of a wound-inducible transcript. The 1.8 kb ACC synthase transcript increased upon wounding the fruit as well as during fruit ripening. Salicylic acid, an inhibitor of wound-responsive genes in tomato, inhibited the wound-induced accumulation of the ACC synthase transcript. Further, polyamines (putrescine, spermidine and spermine) that have anti-senescence properties and have been shown to inhibit the development of ACC synthase activity, inhibited the accumulation of the wound-inducible ACC synthase transcript. The inhibition by spermine was greater than that caused by putrescine or spermidine. The transcript level of a wound-repressible glycine-rich protein gene and that of the constitutively expressed rRNA were not affected as markedly by either salicylic acid or polyamines. These data suggest that salicylic acid and polyamines may specifically regulate ethylene biosynthesis at the level of ACC synthase transcript accumulation.

Base Sequence↗
PubMed1992

Structure and organization of rhodophyte and chromophyte plastid genomes: implications for the ancestry of plastids.

Plastid genomes of two rhodophytes (Porphyra yezoensis and Griffithsia pacifica) and two chromophytes (Olisthodiscus luteus and Ochromonas danica) were compared with one another and with green plants in terms of overall structure, gene complement and organization. The rhodophyte genomes are moderately colinear in terms of gene organization, and are distinguished by three rearrangements that can most simply be explained by transpositions and a large (approximately 40 kb) inversion. Porphyra contains two loci for ppcBA and Griffithsia has two loci for rpoA. Although there is little similarity in gene organization between the rhodophytes and consensus green plant genome, certain gene clusters found in green plants appear to be conserved in the rhodophytes. The chromophytes Olisthodiscus and Ochromonas contain relatively large plastid inverted repeats that encode several photosynthetic genes in addition to the rRNA genes. With the exception of rbcS, the plastid gene complement in Olisthodiscus is similar to that of green plants, at least for the subset of genes tested. The Ochromonas genome, in contrast, appears unusual in that several of the green plant gene probes hybridizing to Olisthodiscus DNA did not detect similar sequences in Ochromonas DNA. Gene organization within the chromophytes is scrambled relative to each other and to green plants, despite the presence of putatively stabilizing inverted repeats. However, some gene clusters conserved in green plants and rhodophytes are also present in the chromophytes. Comparison of the entire rhodophyte, chromophyte and green plant plastid genomes suggests that despite differences in gene organization, there remain overall similarities in architecture, gene content, and gene sequences among in three lineages. These similarities are discussed with reference to the ancestry of the different plastid types.

Biological Evolution↗
PubMed1992

Three new species of the genus Peptostreptococcus isolated from humans: Peptostreptococcus vaginalis sp. nov., Peptostreptococcus lacrimalis sp. nov., and Peptostreptococcus lactolyticus sp. nov.

We describe three new species of the genus Peptostreptococcus which were isolated from human specimens and were tentatively identified as Peptostreptococcus prevotii. These three organisms were not homologous with previously described type strains of the genus Peptostreptococcus. A total of 12 strains that were identified biochemically as P. prevotii were divided into five independent DNA similarity groups; 10 of these strains were divided into three similarity groups which exhibited significant phenotypic differences from previously described species. Therefore, we propose the following new species: Peptostreptococcus vaginalis for group 1 strains, Peptostreptococcus lacrimalis for group 2 strains, and Peptostreptococcus lactolyticus for group 3 strains. The type strain of P. vaginalis is strain GIFU 12669 (= JCM 8138), the type strain of P. lacrimalis is strain GIFU 7667 (= JCM 8139), and the type strain of P. lactolyticus is strain GIFU 8586 (= JCM 8140).

Bacterial Typing Techniques↗
PubMed1992

[Pulmonary function disturbances in patients with hepatic cirrhosis].

The results of five pulmonary function tests on 52 patients with uncompensated hepatic cirrhosis were presented. Compared with matched healthy adults, the patients had decreased values of VC, TLC and DLCO, and their RV/TLC increased (P < 0.05-0.001). Possible pathogenic factors were investigated. The ascites showed evident influences on pulmonary function. In addition to the disorders detected by the above 4 tests, FRC decreased in the patients with ascites. A comparison between the patients with albumin below 30g/L and the patients with albumin above 30g/L revealed that reduced plasma albumin also played role in decreasing VC, TLC and DLCO. Besides the effects of ascites, severe varices of esophagus should have relation to the increase of RV/TLC and the decrease of DLCO.

Adult↗
PubMed1992

[Relationship between Langerhans cells and prognosis of patients with gastric carcinoma].

Langerhans cells (LCs) in 73 cases of gastric carcinomas (GC) were quantitatively investigated by ABC immunohistochemical method using anti-S-100 protein antibody. The mean density of LCs (cell numbers/mm2) infiltrating the carcinomas showed an intimate relationship with the prognosis (P < 0.01) and the status of lymph node (LN) metastasis (P < 0.05). The density of LCs in patients without LN metastasis was significantly higher than that with LN metastasis. In 73 cases of GC, there were 35 cases of LCs(+) and 38 of LCs(++) groups. The mean survival times were 29.81 months in the former and 52.21 months in the latter. A significant relationship (P < 0.05) between the survival and degree of the density of LCs was showed by Student's t test and life table method. There were no correlation among the density of LCs and gross appearance, depth of invasion, histologic type and patients' sex. The fact indicated that LCs may play an important role in immunological defense mechanisms of host against the tumor. Patients with dense infiltration of LCs survived longer and showed less LN metastasis than those without such an infiltration. It is considered that measurement of LCs in specimens of GC may be taken as one of criteria of prognosis.

Antibodies↗
PubMed1992

[Traumatic external gastrointestinal fistula: report of 77 cases].

Seventy-seven patients developed gastroenteric fistula as a complication of abdominal trauma, including small bowl fistula (25), duodenal fistula (17), colonic fistula (16), pancreatic fistula (3), gastric fistula (2), and multiple fistula (14). These patients accounted for 15.9% (77/483) of all patients with intestinal fistula treated in the same period in our department. An average of 8.8 days had elapsed before the final diagnosis of GI fistula was made, during which 73 patients had 1-8 kinds of complications, 48 received 1-5 operations, and 67 were given nutritional support for 6 to 254 days. Thirty patients were cured operatively and 33 (52.4%) spontaneously. The mortality was 18.2%. The etiology, principles of prevention, and management of traumatic intestinal fistula were discussed with emphasis on effective nutritional support and intraabdominal drainage.

Abdominal Injuries↗
PubMed1992

[Research of lectin receptors in early gastric carcinoma].

Sixty cases of early gastric carcinoma (EGC) were studied to identify the receptors against lectins (ConA, DBA, PHA, PNA, and WGA) respectively by means of immunohistochemical ABC technique. The result obtained was coincidently compared with the figures of carcinoembryonic antigen (CEA). Immunoelectronmicroscopy was carried out on four cases with freshly prepared gastric carcinoma specimens in order to observe the distribution of these 5 lectin receptors by using streptavidin-gold complex method. The results were as follows: the gold particles labelled for 5 lectin receptors were mainly located on the cytoplasmic membrane, organelle membrane and the mucin granules. The distribution and the intensity of positive reaction were known to be correlated with histologic typing, histogenesis and the degree of cell differentiation of EGC, PHA, PNA and WGA staining for the corresponding receptors were considered of some value in the diagnosis of gastric carcinoma.

Adenocarcinoma↗
PubMed1992

[The antitumor effect of adriamycin conjugated with monoclonal antibody against gastric cancer in vitro and in vivo].

Adriamycin (ADM), an anthracycline cytotoxic agent, was conjugated with monoclonal antibody 3H11 against gastric cancer via the dextran bridge method. The conjugate 3H11-DEX-ADM, with molar ratio of 3H11 to ADM being 1:73, retained antibody activity to 86%. In the cytotoxicity assay, 3H11-DEX-ADM was shown to exhibit increased cytotoxicity against the target cell line BGC 823. Its IC50 was 3.75 fold less than that of free ADM. The antitumor effect of the conjugate was evaluated in tumor-bearing nude mice. The results indicate that the specific antibody conjugate 3H11-DEX-ADM can significantly inhibit the tumor growth. At the dosage level used in the present study (5 micrograms/mouse x 6), 3H11-DEX-ADM showed an inhibition rate of 51.5%, whereas only moderate inhibition rates were observed with free ADM and the control conjugate NIgG-DEX-ADM. In addition, experiment was performed to evaluate the combined cytotoxicity of 3H11-DEX-ADM and the conjugate of mitomycin C (3H11-HSA-MMC) at different ratios. It was shown that the combination has no synergistic effect when their IC50 was compared with that of the two conjugates used alone. The same result was observed on combinations of the two corresponding free drugs.

Animals↗