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Biomedical subjects

C M Chen

Publications and source records attributed to C M Chen.

At least 235 records · Page 13Linked to original sources
PubMed1990

Molecular biology of carbon-phosphorus bond cleavage. Cloning and sequencing of the phn (psiD) genes involved in alkylphosphonate uptake and C-P lyase activity in Escherichia coli B.

Whereas bacteria such as Escherichia coli have been known for some time to cleave carbon-phosphorus (C-P) bonds in unactivated alkylphosphonates, the enzymes responsible for C-P lyase activity have resisted detection or purification. Genes from E. coli B that support growth on alkylphosphonates as the sole phosphorus source have now been cloned (B. L. Wanner and J. A. Boline, unpublished data). Deletion analysis demonstrated that at least 13 kilobases of DNA information is required for E. coli to express the phosphonate utilization phenotype (Phn+). The complete nucleotide sequence of 15,611 bases has been determined, and the gene structures were examined. Seventeen open reading frames (phnA to phnQ) were identified in one transcriptional direction and five open reading frames in the divergent direction. Sequence homology searches identify PhnC, PhnK, PhnL, and, possibly, PhnN proteins as members of nucleotide-binding proteins of the binding protein-dependent transport systems. Candidates for other membrane components and regulatory proteins are also identified. A Pho box-like promoter sequence is also found upstream of the gene cluster starting at phnA, which is consistent with the observation of phosphate regulation of the Phn+ response. Fourteen repetitive extragenic palindromic sequences are found in the phn DNA: 10 exist in the extragenic region between phnA and phnB, two between phnD and phnE, and two between phnK and phnL. An unusual finding is that one of the repetitive extragenic palindromic sequences actually overlaps with the reading frame of the phnE gene.

Amino Acid Sequence↗
PubMed1990

Cytokinin enhancement of the light induction of nitrate reductase transcript levels in etiolated barley leaves.

To investigate the molecular mechanism of cytokinin regulation of nitrate reductase (NR) activity, the influence of benzyladenine (BA) on the level of NR transcript was studied in etiolated barley leaves using a barley NR cDNA as a probe. Northern blot analyses of the levels of NR poly (A)+ RNA indicate that the amount present is proportional to the concentration of BA (2 x 10(-8) to 2 x 10(-4) M) applied to the leaves. Enhancement of NR mRNA by 2 x 10(-5) M BA was clearly detected after 15 minutes of exposure of the leaves to light. The enhancement is cytokinin-specific and adenine is ineffective. Brief treatment with the protein synthesis inhibitor, cycloheximide, inhibited BA-enhanced NR activity but did not inhibit BA-enhanced NR transcript level, thus the enhancement was independent of concurrent protein synthesis. Nuclear runoff transcription studies showed that the enhancement of NR mRNA was at least partially due to increased transcription rates.

Adenine↗
PubMed1990

Cloning, expression, and purification of human cyclophilin in Escherichia coli and assessment of the catalytic role of cysteines by site-directed mutagenesis.

The cDNA encoding human cyclophilin from the Jurkat T-cell lymphoma line has been cloned by the expression cassette polymerase chain reaction and sequenced, and an expression vector has been constructed under control of the tac promoter for efficient expression in Escherichia coli. Active cyclophilin is produced at up to 40% of soluble cell protein, facilitating a one-column purification to homogeneity. Wild-type cyclophilin was characterized for binding of the potent immunosuppressant agent cyclosporin A (Kd = 46 nM) by tryptophan fluorescence enhancement and for inhibition (IC50 = 19 nM) of cyclophilin's peptidyl-prolyl cis-trans isomerase (rotamase) activity. With N-succinyl-Ala-Ala-Pro-Phe-p-nitroanilide as the substrate, recombinant human cyclophilin has a high catalytic efficiency; kcat/Km is 1.4 X 10(7) M-1.S-1 at 10 degrees C. To test the prior suggestion that a cysteine residue may be essential for catalysis and immunosuppressant binding, the four cysteines at positions 52, 62, 115, and 161 were mutated individually to alanine and the purified mutant proteins were shown to retain full affinity for cyclosporin A and equivalent catalytic efficiency as a rotamase. Clearly the cysteines play no essential role in catalysis or cyclosporin A binding. These results rule out the recently proposed mechanism [Fischer, G., Wittmann-Liebold, B., Lang, K., Kiefhaber, T. & Schmid, F. X. (1989) Nature (London) 337, 476-478)] involving the formation of tetrahedral hemithioorthoamide. Whereas mechanisms that embody other tetrahedral intermediates may be operative, an alternative mechanism is considered that involves distortion of bound substrate with a twisted (90 degrees) peptidyl-prolyl amide bond.

Animals↗
PubMed1990

Identification of a human stomach alcohol dehydrogenase with distinctive kinetic properties.

A new form of alcohol dehydrogenase, designated mu-alcohol dehydrogenase, was identified in surgical human stomach mucosa by isoelectric focusing and kinetic determinations. This enzyme was anodic to class I (alpha, beta, gamma) and class II (pi) alcohol dehydrogenases on agarose isoelectric focusing gels. The partially purified mu-alcohol dehydrogenase, specifically using NAD+ as cofactor, catalyzed the oxidation of aliphatic and aromatic alcohols with long chain alcohols being better substrates, indicating a barrel-shape hydrophobic binding pocket for substrate. mu-Alcohol dehydrogenase stood out in high Km values for both ethanol (18 mM) and NAD+ (340 microM) as well as in high Ki value (320 microM) for 4-methylpyrazole, a competitive inhibitor for ethanol. mu-Alcohol dehydrogenase may account for up to 50% of total stomach alcohol dehydrogenase activity and appeared to play a significant role in first-pass metabolism of ethanol in human.

Alcohol Dehydrogenase↗
PubMed1990

[Effects of anisodamine on blood coagulation, fibrin and thrombosis in rabbits].

Anisodamine at dose of iv 10 and 20 mg/kg prolonged plasma prothrombin time, bleeding time and coagulation time, and showed positive reaction of plasma protamine paracoagulation test in conscious rabbits. The drug prolonged the thrombin time and reduced the contend of plasma fibrin. Anisodamine markedly inhibited blood platelet aggregation both in vitro and in vivo, dose-dependently. The extracorporeal thrombosis time was prolonged, the length and weight of thrombus was decreased after iv anisodamine 20 mg/kg. These results suggest that anisodamine has inhibitory action thrombosis and blood coagulation.

Animals↗
PubMed1989

Novel metabolism of several beta zero-thalassemic beta-globin mRNAs in the erythroid tissues of transgenic mice.

Mice that are transgenic for human beta zero-thalassemic beta-globin alleles were generated in order to study how beta zero-thalassemic mutations affect beta-globin RNA metabolism in erythroid tissues. Three thalassemic alleles were studied, each of which harbors either a frameshift or a nonsense mutation. These mutations result in the premature termination of beta-globin mRNA translation and an abnormally low level of beta-globin mRNA in the peripheral blood of thalassemic patients. Comparative studies of mice that express any of the beta zero-thalassemic transgenes with mice that express a normal human beta-globin transgene demonstrated that all three thalassemic mRNAs are metabolized in erythroid tissues abnormally. RNA blotting and S1 nuclease transcript mapping revealed for each thalassemic transgene that (i) the full-length mRNA is abnormally short-lived and (ii) in addition to full-length mRNA, three more stable yet smaller RNAs are present. These smaller RNAs are polyadenylated and lack the mRNA 5' end.

Animals↗
PubMed1989

Decreased resistance to Listeria monocytogenes in mice following vanadate exposure: effects upon the function of macrophages.

We have previously demonstrated that ammonium metavanadate has a broad immunomodulating effect in mice after subchronic exposure. Because host resistance to pathogenic Listeria monocytogenes and in vitro phagocytic activity of harvested peritoneal macrophages (PEM) were strongly affected by vanadate treatment, we investigated the effect of vanadate on the functional role of resident PEM in active listeriosis in the mouse. Vanadium treatment results in altered patterns of clearance of the organism from the peritoneal cavity, liver and spleen. The total in vitro phagocytic uptake of Listeria by PEM was consistently decreased as a function of infection period. Similarly, intracellular killing of Listeria was decreased although the PEM from the vanadate-treated and control mice were more bacteriostatic than bactericidal. Population distributions of Listeria within infected PEM were not affected by host pretreatment with vanadate. Vanadate exposure interferes with both the uptake and ultimate intraphagolysosomal killing of Listeria. These results were expected in light of our previous studies of the effects of vanadate on PEM superoxide production, and hexose monophosphate shunt and glutathione redox cycle activity. The results provide additional information for the development of a mechanism to explain why workers exposed to vanadium-containing dusts have increased susceptibility to bacterial respiratory diseases.

Animals↗
PubMed1989

Altered imino diacid synthesis and transcription in crown gall tumors with transposon Tn5 insertions in the 3' end of the octopine synthase gene.

Octopine synthase encoded by the T-DNA (transferred DNA) locus ocs synthesizes N2-(D-1-carboxyethyl)-L-amino acids in octopine-type crown gall tumors. So far, derivatives of only basic amino acids have been isolated. We have detected a glutamine derivative and called it heliopine. Tumors induced by several Ti plasmids with transposon Tn5 insertions in the 3' end of ocs still synthesized small quantities of N2-(1-carboxyethyl)-arginine and N2-(1-carboxyethyl)-glutamine. In addition, N2-(1,3-dicarboxypropyl)-asparagine, which is absent in wild-type octopine tumors, was detected in these tumors. These three imino diacids (octopine, heliopine, and asparaginopine, respectively, or their isomers) were undetectable in tumors induced by Ti plasmids harboring deletions of the ocs gene. Poly(A)+ RNAs which hybridize to the ocs sequence can also be detected in the ocs::Tn5 tumors; these RNAs, however, were heterogeneous in size and shorter in length than the normal ocs mRNA. These results indicate that mutant ocs products synthesize imino diacids in these ocs::Tn5 tumors.

Amino Acid Oxidoreductases↗
PubMed1988

In vitro induction of differentiation in HL-60 leukemic cell line by clerodendron fragrans.

The promyelocytic cell line HL-60 could be induced to differentiate into morphologically and functionally mature monocytoid cells (up to 20%) following exposure to the Chinese herb Clerodendron Fragrans (1 mg/ml). This effect was time dependent and appeared to work synergistically with interferon-r in this promotion of differentiation. Our study suggests that Clerodendron Fragrans has potential therapeutic value for the treatment of certain acute myelocytic leukemia putatively caused by a block in the myeloid differentiation process.

Cell Differentiation↗
PubMed1988

Biomechanical analysis of stability and fixation strength of total shoulder prostheses.

The Neer I (polyethylene glenoid), Neer II (plastic glenoid surface with metal backing), Cofield, and Gristina monospherical total shoulder prostheses were tested for joint subluxation resistance and glenoid component fixation strength. Synthetic glenoid models with consistent structural properties and standard under-cutting geometry were used for glenoid component fixation with bone cement. It was found that joint subluxation resistance varied linearly with axial compressive force applied. Higher subluxation strength was associated with the amount of curvature of the glenoid articulating surface. Consequently, joint stability was consistently higher for the Gristina design, and all had lower resistance in the anteroposterior direction. After complete joint dislocation under high axial compressive force, the polyethylene material at the site of subluxation experienced gross plastic deformation. The fixation strength of the glenoid component was lowest for the Neer I design and highest for the Cofield design. Fatigue loading at the joint did not seem to affect the glenoid component fixation strength. In general, all glenoid components appeared to have sufficient fixation strength against normal shoulder joint forces except the Neer I design. Loosening and fracture of the plastic glenoid component may occur under excessive loads.

Biomechanical Phenomena↗
PubMed1988

Studies on hexachlorocyclohexane and DDT contents in human cerumen and their relationships to cancer mortality.

Organochlorine pesticides in cerumen were used as a biological marker to monitor the exposure of organochlorine pesticides in the human body. The amount of sample used was about 10 mg. The order of magnitude of HCH (hexachlorocyclohexane) isomer content in cerumen was beta greater than alpha greater than gamma greater than delta; for DDT, the order was p,p'-DDE greater than p,p'-DDT. There was little o,p'-DDT and p,p'-DDD. The contents of beta-HCH and p,p'-DDE in cerumen were highly significantly correlated with those in adipose tissue of the same individuals. Approximately 3800 cerumen samples collected from 35- to 54-year-old healthy adults in the general populations of 35 counties were analyzed for HCH and DDT. The accumulation levels of beta-HCH had a geographical character with obvious gradient differences, and the levels were higher in males than in females. The accumulation levels of beta-HCH in the populations studied were highly significantly correlated with the mortality rates from liver cancer, colon/rectum cancer, and lung cancer in males as well as colon/rectum cancer in females (P less than 0.01), suggesting that the effect of HCH on the above cancers should be studied further.

Adipose Tissue↗
PubMed1988

Rapid identification of monoclonal antibodies to differential antigens by dot immunobinding assay.

A simple and highly sensitive method, dot immunobinding assay, has been developed to select of monoclonal antibodies recognizing differential antigens. Antigen as low as picogram level can be detected by monoclonal antibody at concentrations even lower than 0.1 microgram/ml. This technique has successfully identified six differential antigens which are either increased (three) or decreased (three) during T cell activation. The differential properties were further confirmed by direct visualization of the resting and activated T cells with immunofluorescent staining or by indirect evidence when resting and activated T cell extracts were prepared and analysed with immunoblot assay. CC-98 (105 KD) was found in the nuclei, principally associated with the nucleoli. Activated T cells expressed a highly intense immunofluorescent pattern at their nucleolar localization compared to that of resting T cells. SH-1 antigen with a diffuse molecular weight range of 90-145 KD was expressed mainly in resting T cells and rapidly decreased, especially the high molecular weight species (120-145 KD), to a very low level in the activated T cells. SH-1 was identified as an intracellular molecule. NY-16 and CC-262 are identical with characteristics ascribed to those of the major histocompatibility class I antigen. Cell surface molecules CC-80 (135 KD) and CC-86 (135 KD) were decreased, while CC-196 was increased during T cell activation. These six molecules, with their differentiating properties, may have very important functions related to cell activation.

Animals↗
PubMed1987

[Respiratory function and pulmonary thromboxane release after total thoracic esophagectomy].

In experimental studies using mongrel dogs, 60 minutes after total thoracic esophagectomy the dog lung transiently released into the systemic circulation up to about 6000 micrograms/ml of thromboxane A2(TXA2) measured by radioimmunoassay as its metabolite thromboxane B2(TXB2). To determine whether lung TX release had effects on pulmonary function, we measured the changes in extravascular lung water (EVLW), lung resistance (RL) before, 10, 30, and 60 minutes after total thoracic esophagectomy in 14 anesthetized dogs. In seven untreated dogs, EVLW and RL increased and CL decreased approximately twofold at 60 minutes after the surgery, which corresponded well with a large transpulmonary plasma concentration gradient of TXB2. In remaining 7 dogs pretreated with intravenous OKY-046 which was TXA2 synthetase inhibitor, increase in EVLW and RL and decrease in CL were minimal and plasma concentration of TXB2 remained low value of a preoperative level. In clinical studies, 20 patients with esophageal carcinoma were evaluated. All of these patients underwent total thoracic esophagectomy with extended lymph node dissection of a similar extent. In 5 control patients, significant increase in EVLW and pulmonary vascular resistance were noted at 60 minutes after surgery. On the other hand, while the patients who had intravenous OKY-046 administration during operation at a dose of 1 microgram/kg/min or 5 micrograms/kg/min showed significant decrease in EVLW and pulmonary vascular resistance at 60 minutes after surgery. Based on these results, it is concluded that TXA2 appears to be one of the most important factors to cause the postoperative pulmonary complication after total thoracic esophagectomy for esophageal cancer.

Animals↗