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Biomedical subjects

L Zhu

Publications and source records attributed to L Zhu.

At least 451 records · Page 25Linked to original sources
PubMed1993

[Gastric mucosal blood flow and blood viscosity in patients with diabetes].

For the study of the microcirculatory disturbance of the digestive tract in patients with diabetes, 41 cases with non-insulin dependent diabetes mellitus (NIDDM) were selected (mean age 53.9 Yrs., 22 male/19 female). Of these patients 9 were without complication, and 32 with complications. Gastric mucosal blood flow (GMBF) was determined at 14 points of laser and greater curvature, anterior and posterior wall of antrum, angle and corpus of stomach, pylorus and anterior wall of duodenum with laser Doppler flowmetry (PF2). Results showed that the mean value of the 14 points of GMBF in 41 patients with NIDDM was 2.81 +/- 0.15(V, mean +/- s mean), which was significantly lower than that of 11 normal subjects (4.77 +/- 0.29V, P < 0.001). The mean GMBF of 8 cases of NIDDM without gastric disease was 2.92 +/- 0.28V, which was also lower than that of normal control (61.2% of normal value, P < 0.001). The GMBF in 27 cases of diagnosed chronic superficial gastritis (CSG 2.79 +/- 0.15V) was lower than the GMBF of 63 CSG patients without NIDDM (3.23 +/- 0.12V, P < 0.05). The viscosity of blood and plasma was determined with NAAKE viscometer in 26 patients with NIDDM. It was found that the blood viscosity was significantly higher than that of the normal control, and the plasma viscosity was also increased but without statistic significance. Results showed that the GMBF of NIDDM was significantly lower than that of the normal subjects or CSG patients without diabetes. It implied that the visceral microcirculatory disturbance also involved the digestive system leading to the GMBF decrease.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1993

Amplification and analysis of a male-specific SRY homologous sequence of cattle.

Based on the highly conserved region of human, rabbit and mouse SRY (sex-determining region Y) sequences, primers were designed for the amplification of the unknown homologous sequence of cattle by polymerase chain reaction (PCR). A 200-bp male-specific amplifying fragment was obtained. The fragment shares high homology with the known SRY gene. By using the cloned fragment as a probe to hybridize to the Southern blot of HindIII-digested cattle genomic DNA, a 1.7-kb male-specific fragment was detected, which is considered to contain the 200-bp fragment. When the same pair of primers was used in amplification of human and goat DNA samples, the 200-bp male-specific fragment could be detected.

Animals↗
PubMed1993

[Distribution of the intermediate filaments in rat Sertoli cells: an electron microscopic study].

The distribution of intermediate filaments (IFs) in the Sertoli cells of rat testis was studied under a transmission electron microscope. The results showed that IFs in Sertoli cells were centrally arranged around the nucleus in a criss-cross manner. From the perinuclear region the IFs had widespread extensions and were connected with the following structures: 1) with the mitochondria, Golgi apparatus, endoplasmic reticulum and other subcellular structures; 2) with the desmosome-like and hemi-desmosome-like junctions with adjacent Sertoli and spermatogenic cells; 3) with the microfilaments (MFs) in the ectoplasmic specialization (ES) surrounding the head of elongated stage I-V; spermatids; 4) with the MFs in ES between adjacent Sertoli cells. In conclusion, IFs form a delicate intracellular network in Sertoli cell with its center in the perinuclear region and stretching and connecting with many subcellular structures in the cytoplasm and cell membrane.

Animals↗
PubMed1993

[Typing on 5'-terminal noncoding region of hepatitis C virus genome with restrict endonuclease].

We reported typing of the 5'-terminal noncoding region of HepCV genome in 219 patients with hepatitis C using restrict endonuclease. These patients came from different areas of China. The infective percentage of HCV type II was 83%, type III 14%, and mixed type II and III (II/III) 2%. It is indicated that type III and II/III. The constituent rate of HCV subgenome type in different areas was not significantly different.

China↗
PubMed1992

Peroxynitrite-mediated tyrosine nitration catalyzed by superoxide dismutase.

Peroxynitrite (ONOO-), the reaction product of superoxide (O2-) and nitric oxide (NO), may be a major cytotoxic agent produced during inflammation, sepsis, and ischemia/reperfusion. Bovine Cu,Zn superoxide dismutase reacted with peroxynitrite to form a stable yellow protein-bound adduct identified as nitrotyrosine. The uv-visible spectrum of the peroxynitrite-modified superoxide dismutase was highly pH dependent, exhibiting a peak at 438 nm at alkaline pH that shifts to 356 nm at acidic pH. An equivalent uv-visible spectrum was obtained by Cu,Zn superoxide dismutase treated with tetranitromethane. The Raman spectrum of authentic nitrotyrosine was contained in the spectrum of peroxynitrite-modified Cu,Zn superoxide dismutase. The reaction was specific for peroxynitrite because no significant amounts of nitrotyrosine were formed with nitric oxide (NO), nitrogen dioxide (NO2), nitrite (NO2-), or nitrate (NO3-). Removal of the copper from the Cu,Zn superoxide dismutase prevented formation of nitrotyrosine by peroxynitrite. The mechanism appears to involve peroxynitrite initially reacting with the active site copper to form an intermediate with the reactivity of nitronium ion (NO2+), which then nitrates tyrosine on a second molecule of superoxide dismutase. In the absence of exogenous phenolics, the rate of nitration of tyrosine followed second-order kinetics with respect to Cu,Zn superoxide dismutase concentration, proceeding at a rate of 1.0 +/- 0.1 M-1.s-1. Peroxynitrite-mediated nitration of tyrosine was also observed with the Mn and Fe superoxide dismutases as well as other copper-containing proteins.

Animals↗
PubMed1992

Kinetics of superoxide dismutase- and iron-catalyzed nitration of phenolics by peroxynitrite.

Superoxide dismutase and Fe3+EDTA catalyzed the nitration by peroxynitrite (ONOO-) of a wide range of phenolics including tyrosine in proteins. Nitration was not mediated by a free radical mechanism because hydroxyl radical scavengers did not reduce either superoxide dismutase or Fe3+EDTA-catalyzed nitration and nitrogen dioxide was not a significant product from either catalyst. Rather, metal ions appear to catalyze the heterolytic cleavage of peroxynitrite to form a nitronium-like species (NO2+). The calculated energy for separating peroxynitrous acid into hydroxide ion and nitronium ion is 13 kcal.mol-1 at pH 7.0. Fe3+EDTA catalyzed nitration with an activation energy of 12 kcal.mol-1 at a rate of 5700 M-1.s-1 at 37 degrees C and pH 7.5. The reaction rate of peroxynitrite with bovine Cu,Zn superoxide dismutase was 10(5) M-1.s-1 at low superoxide dismutase concentrations, but the rate of nitration became independent of superoxide dismutase concentration above 10 microM with only 9% of added peroxynitrite yielding nitrophenol. We propose that peroxynitrite anion is more stable in the cis conformation, whereas only a higher energy species in the trans conformation can fit in the active site of Cu,Zn superoxide dismutase. At high superoxide dismutase concentrations, phenolic nitration may be limited by the rate of isomerization from the cis to trans conformations of peroxynitrite as well as by competing pathways for peroxynitrite decomposition. In contrast, Fe3+EDTA appears to react directly with the cis anion, resulting in greater nitration yields.

Animals↗
PubMed1992

Peroxynitrite formation from macrophage-derived nitric oxide.

Peroxynitrite formation by rat alveolar macrophages activated with phorbol 12-myristate 13-acetate was assayed by the Cu,Zn superoxide dismutase-catalyzed nitration of 4-hydroxyphenylacetate. The inhibitor of nitric oxide synthesis N-methyl-L-arginine prevented the Cu,Zn superoxide dismutase-catalyzed nitration of 4-hydroxyphenylacetate by stimulated macrophages, while Cu-depleted Zn superoxide dismutase did not catalyze the formation of 3-nitro-4-hydroxyphenylacetate either in vitro or in the presence of activated macrophages. The rate of phenolic nitration by activated macrophages was 9 +/- 2 pmol x 10(6) cells-1 x min-1 (mean +/- STD). Only 8% of synthetic peroxynitrite was trapped by superoxide dismutase, which suggested that the rate of peroxynitrite formation may have been as high as 0.11 nmol x 10(6) cells-1 x min-1. This upper estimate was consistent with N-methyl-L-arginine increasing the amount of superoxide detected with cytochrome c by 0.12 nmol x 10(6) cells-1 x min-1. The rate of nitrite and nitrate accumulation was 0.10 +/- 0.001 nmol x 10(6) cells-1 x min-1, suggesting that the majority of nitric oxide produced by activated macrophages may have been converted to peroxynitrite. The formation of a relatively long lived, strong oxidant from the reaction of nitric oxide and superoxide in activated macrophages may contribute to inflammatory cell-mediated tissue injury.

Animals↗
PubMed1992

Bactericidal activity of peroxynitrite.

Peroxynitrite is a strong oxidant formed by macrophages and potentially by other cells that produce nitric oxide and superoxide. Peroxynitrite was highly bactericidal, killing Escherichia coli in direct proportion to its concentration with an LD50 of 250 microM at 37 degrees C in potassium phosphate, pH 7.4. The apparent bactericidal activity of a given concentration peroxynitrite at acidic pH was less than that at neutral and alkaline pH. However, after taking the rapid pH-dependent decomposition of peroxynitrite into account, the rate of the killing was not significantly different at pH 5 compared to pH 7.4. Metal chelators did not decrease peroxynitrite-mediated killing, indicating that exogenous transition metals were not required for toxicity. The hydroxyl radical scavengers mannitol, ethanol, and benzoate did not significantly affect toxicity while dimethyl sulfoxide enhanced peroxynitrite-mediated killing. Dimethyl sulfoxide is a more efficient hydroxyl radical scavenger than the other three scavengers and increased the formation of nitrogen dioxide from peroxynitrite. In the presence of 100 mM dimethyl sulfoxide, 60.0 +/- 0.3 microM nitrogen dioxide was formed from 250 microM peroxynitrite as compared to 2.0 +/- 0.1 microM in buffer alone. Thus, formation of nitrogen dioxide may have enhanced the toxicity of peroxynitrite decomposing in the presence of dimethyl sulfoxide.

Anti-Bacterial Agents↗
PubMed1992

The Escherichia coli rna gene encoding RNase I: sequence and unusual promoter structure.

A clone containing the Escherichia coli rna gene encoding the nonspecific endoribonuclease, RNase I, was isolated and sequenced. The sequence of the 1070-nucleotide (nt) fragment agreed completely with that of a rna clone recently reported by Meador and Kennell [Gene 95 (1990) 1-7]. The transcription start point (tsp) of rna was identified using primer extension analysis, and its promoter sequence was established by comparison of RNase I expression levels in various deletion mutants. Our results indicate that the rna promoter is highly unusual. Its -35 region shows a poor match to the consensus sequence, and moreover, it is located within a stem-loop structure that apparently is a Rho-independent transcription termination site for an upstream gene.

Base Sequence↗
PubMed1992

Human erythrocyte protein 4.2: isoform expression, differential splicing, and chromosomal assignment.

Human protein 4.2 (P4.2) is a major membrane skeletal protein in erythrocytes. Individuals with P4.2 deficiency exhibit spherocytosis and experience various degrees of hemolytic anemia, suggesting a role for this protein in maintaining stability and integrity of the membrane. Molecular cloning of P4.2 cDNAs showed that P4.2 is a transglutaminaselike molecule in erythrocytes but lacks the essential cysteine for cross-linking activity. Two cDNA isoforms have been identified from a human reticulocyte cDNA library, with the long isoform containing a 90-base pair (bp) in-frame insertion encoding an extra 30 amino acids near the N-terminus. Characterization of the P4.2 gene suggests differential splicing as the mechanism for generating these two cDNA isoforms. The donor site for the short isoform (P4.2S) agrees better with the consensus than the donor site for the long isoform (P4.2L) does. Expression of P4.2L was detected by a long-isoform-specific antibody raised against a peptide within the 30-amino acid insert. Western blot analyses showed P4.2L to be a minor membrane skeletal protein in human erythrocytes with an apparent molecular weight (mol wt) of approximately 3 Kd larger than the major protein 4.2, P4.2S. By in situ hybridization of a full-length 2.4-kilobase (kb) cDNA to human metaphase chromosomes, the gene for P4.2 was mapped to bands q15-q21 of chromosome 15, and it is not linked to the gene for coagulation factor XIIIa (plasma transglutaminase, TGase).

Amino Acid Sequence↗
PubMed1992

Conformational interconversion in protein crystals.

We present evidence that the structure of carbonmonoxy myoglobin crystals can be altered by lowering the pH. This structural change is monitored by the characteristic Fe-CO Raman modes at 508 and 491 cm-1 and is thought to involve a localized distal pocket transition from a "closed" conformation at pH 7 to a more "open" conformation at pH 4. These changes take place in the crystal without loss of intensity of a conformationally sensitive Raman mode at 252 cm-1 that signals a partial unfolding of the globin structure in solution. Quantitative studies, which monitor the open and closed populations as a function of laser photolysis, demonstrate that the interconversion rates (k+/-) in solution at 298 K are fast compared to the photolysis and CO entry rates (i.e. k+/- much greater than 10(3) s-1), while in frozen samples the interconversion is much slower than the experimental time scale (minutes). Since the open conformation is a minority species at pH 7, rapid exchange in aqueous solution is a necessary condition for this species to play a functional role. In the crystal, the interconversion rates are slowed compared to solution and begin to approach the photolysis rate (i.e. k+/- approximately 10(3) to 10(4) s-1). This indicates that the barriers for conformational exchange are increased in the crystal environment, compared to the solution, apparently due to the packing forces of the surrounding molecules. X-ray and neutron diffraction studies of MbCO crystals at high and low pH are needed to characterize the details of the structural changes and to test the hypothesis that closed and open distal pocket structures are associated with the 508 and 491 cm-1 Fe-CO modes.

Hydrogen-Ion Concentration↗
PubMed1992

Molecular cloning of the cDNA for the catalytic subunit of human DNA polymerase delta.

The cDNA of human DNA polymerase delta was cloned. The cDNA had a length of 3.5 kb and encoded a protein of 1107 amino acid residues with a calculated molecular mass of 124 kDa. Northern blot analysis showed that the cDNA hybridized to a mRNA of 3.4 kb. Monoclonal and polyclonal antibodies to the C-terminal 20 residues specifically immunoblotted the human pol delta catalytic polypeptide. A multiple sequence alignment was constructed. This showed that human pol delta is closely related to yeast pol delta and the herpes virus DNA polymerases. The levels of pol delta message were found to be induced concomitantly with DNA pol delta activity and DNA synthesis in serum restimulated proliferating IMR90 cultured cells. The human pol delta gene was localized to chromosome 19 by Southern blotting of EcoRI digested DNA from a panel of rodent/human cell hybrids.

Amino Acid Sequence↗
PubMed1992

Synthesis and cytotoxic evaluation of some 6-arylidene-2-(alpha-hydroxyamino-alpha-arylmethyl)cyclohexanone oximes and related compounds.

Reaction of 2,6-bis-(phenylmethylene)cyclohexanone (1) with a 4-molar excess of hydroxylamine hydrochloride and sodium acetate to produce the corresponding oxime 2 gave rise to 2-(alpha-hydroxyamino-alpha-phenylmethyl)-6-phenylmethylenecyclohexan one oxime (5a), whose structure was deduced from high-resolution proton nuclear magnetic resonance spectroscopy and confirmed by X-ray analysis. Compound 2 was eventually prepared from 1 with hydroxylamine per se and not with a mixture of hydroxylamine hydrochloride and sodium acetate. Ten analogues of 5a, namely 5b-5k, were prepared and evaluated for cytotoxicity. Six of the 11 compounds in series 5, as well as 1, showed activity in the 240-950 microM range against murine mammary EMT6 cells. Series 5 was also examined for cytotoxicity in an in vitro screen conducted by the National Cancer Institute with approximately 54 cell lines, and four compounds demonstrated selective toxicity toward various groups of tumors.

Animals↗
PubMed1992

Functional organization of enhancer (ENII) of hepatitis B virus.

A new enhancer ENII, located in the X open reading frame and immediately upstream of the core gene promoter, has recently been identified in the genome of hepatitis B virus. We have studied the functional constituents of this new enhancer in different cell lines. ENII can be divided into two functional elements, A and B, corresponding to two major binding sequences for nuclear protein factors. Element A alone gave very low activity; however, it was a modulatory element important for cell-type specificity. Element B was shown to be the basic functional element of ENII, which retained about 70% of the enhancer activity of the complete ENII in HepG2 cells. Element B can be further dissected into three subunits, B1, B2, and B3, which act synergistically. A 52-bp sequence is identified as the core sequences of element B. A model for the mechanism of ENII function is proposed.

Base Sequence↗
PubMed1992

Albumin in the cornea is oxidized by hydrogen peroxide.

The action of hydrogen peroxide on soluble proteins of the rat cornea has been evaluated. Two major corneal proteins are found to be oxidized by 10 mM hydrogen peroxide. Protein sequence and antibody recognition has shown one of the proteins to be albumin. Treatment of pure rat or human albumin with hydrogen peroxide oxidizes the protein and decreases its affinity for its antibody. Because albumin is a major protein in the cornea, its ready oxidation suggests that a role for albumin in this tissue may be to act as a native antioxidant, scavenging hydrogen peroxide and thus preventing more extensive damage by this toxin. These data are relevant to the evaluation of the safety of contact lens disinfectants containing hydrogen peroxide and suggest that further study of the action of this oxidant is warranted.

Albumins↗
PubMed1992

[Influence of 5.7-dihydroxytryptamine on electro-acupuncture analgesia and substance P level in central nervous system of the arthralgic rats].

The relation between electroacupuncture (EA) analgesia (A) and substance P (SP) level in the brain stem (BS) and lumbar spinal cord (LSC) of arthralgic rats was investigated. The rats were divided into three groups: 1)5.7-dihydroxytryptamine (5.7-DHT) + EA, 2) vehicle (V) + EA, and 3)5.7-DHT. All the animals were induced arthralgesia by injecting Freund's adjuvant 7 days after cisterna injection of 5.7-DHT or vehicle. The SP level in the BS and LSC was determined by RIA. The results indicated that in V + EA group the EA could prolong tail flick latency by 39.6%, but in other two groups did not. The SP level in LSC of V + EA group (179.1 +/- 11.5 pmol/g) was higher than that in the 5.7-DHT + EA (135.9 +/- 9.3pmol/g) and 5.7-DHT (125.8 +/- 10.0 pmol/g) groups. It suggested that both EA and arthralgia could activate the descending 5-HTergic inhibitory system to inhibit the release of SP in LSC. When the 5-HTergic system was destroyed by 5.7-DHT, the EAA was attenuated, and the SP level in LSC was lowered due to its release was decreased by EA and arthralgia.

Acupuncture Analgesia↗