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Biomedical subjects

X M Li

Publications and source records attributed to X M Li.

At least 217 records · Page 12Linked to original sources
PubMed1985

Characterization of nine monoclonal antibodies against the Escherichia coli cyclic AMP receptor protein.

Nine hybridoma clones producing antibodies against the Escherichia coli cAMP receptor protein (CRP) have been isolated. Five of the monoclonal antibodies (Class I) had a much higher affinity for native CRP while the remaining four (Class II) bound equally well to native or denatured CRP. Using native N-terminal CRP cores, it was shown that none of the Class I monoclonal antibodies cross-reacted with the 15,000-Da CRP core, and only two bound to the 18,800-Da CRP core. The positions of the antigenic determinants for the Class II monoclonal antibodies were found by Western blotting analysis to reside in the N-proximal region of CRP. Only one monoclonal antibody strongly inhibited cAMP binding by CRP, and this was accompanied by a consequent strong inhibition of both lac DNA binding and abortive initiation by RNA polymerase. Each of the Class I monoclonal antibodies inhibited abortive initiation, and four of these antibodies also blocked the binding of cAMP X CRP to the lac DNA fragment. One Class I and one Class II monoclonal antibody bound to the cAMP X CRP X DNA complex. Two of the Class II monoclonal antibodies were without apparent effect on any of the assays used.

Animals↗
PubMed1984

Inhibition of platelet phosphatidylinositol synthetase by an analog of CDP-diacylglycerol.

Unpublished portions of the synthesis of a phosphinate-phosphonate diether analog of CDPdiacylglycerol are reported. The liponucleotide analog was found to be a very powerful inhibitor of platelet PI synthetase; kinetic data suggest a competitive inhibition mechanism. The structural specificity of CDPdiacylglycerol for liponucleotide-mediated biosynthetic reactions is discussed.

Blood Platelets↗
PubMed1984

Primary structural sequence polymorphism in the human class II MHC antigen 33.1.

Monoclonal antibody 33.1 defines a non-DR, class II, human major histocompatibility complex antigen, 33.1, which appears to be distinct from other class II antigens in its cellular distribution and primary structure. To characterize the structure more fully and to determine the degree of polymorphism within 33.1, a comparative N-terminal sequence study has been undertaken using a series of ten B lymphoblastoid cell lines with different DR and MB types. The results confirm that both the alpha and beta chains of 33.1 are homologues of the corresponding chains of the murine I-A antigen and indicate that while 33.1 does not appear to be identical with MB, it is closely related. Sequence analyses revealed two major variants of 33.1, corresponding to cells with specificities MB1 and MB3, respectively. Within each MB type, other polymorphisms have been detected. Cells that are MB2 do not react with monoclonal antibody 33.1. Suggestive evidence is presented that monoclonal antibody 33.1 reacts predominantly with the beta chain of the antigen. The preferential expression of 33.1 on activated B cells suggests that expression of at least the 33.1 beta chain gene is greatly enhanced in the course of B-cell activation, but the specific function of 33.1 remains to be determined.

Amino Acid Sequence↗
PubMedDate not supplied

The use of protein synthesis elongation factor EF-Tu as internal calibration standard in two-dimensional electrophoretic studies of differentiation in Streptomyces.

Protein synthesis elongation factor EF-Tu is presented as an internal calibration standard for quantitative analysis of two-dimensional (2-D) protein electrophoresis gels. EF-Tu was selected on the basis of concentration measurements in cell-free extracts from Streptomyces aureofaciens, grown under conditions leading to production of tetracyclines, and separated on one-dimensional (1-D) and 2-D electrophoresis gels. The results demonstrated that the amount of EF-Tu synthesized in S. aureofaciens under conditions of slow growth during production of tetracyclines is constant in proportion to all other de novo synthesized proteins regardless of their total number. This makes EF-Tu an ideal internal protein standard for quantitation of protein spots on 2-D electrophoresis gels. For such quantitative analysis we developed a computer-aided image analysis system which provides preparation of a gel image for further analysis including calibration, background subtraction and cleaning for streaking in both directions. The system can locate any resolvable spot in the gel and measure the integrated density of the spot, even in the case of irregular spot shape in crowded and overlapping spot regions.

Biomarkers↗
PubMedDate not supplied

Receptor-receptor interactions as an integrative mechanism in nerve cells.

Several lines of evidence indicate that interactions among transmission lines can take place at the level of the cell membrane via interactions among macromolecules, integral or associated to the cell membrane, involved in signal recognition and transduction. The present view will focus on this last subject, i.e., on the interactions between receptors for chemical signals at the level of the neuronal membrane (receptor-receptor interaction). By receptor-receptor interaction we mean that a neurotransmitter or modulator, by binding to its receptor, modifies the characteristics of the receptor for another transmitter or modulator. Four types of interactions among transmission lines may be considered, but mainly intramembrane receptor-receptor interactions have been dealt with in this article, exemplified by the heteroregulation of D2 receptors via neuropeptide receptors and A2 receptors. The role of receptor-receptor interactions in the integration of signals is discussed, especially in terms of filtration of incoming signals, of integration of coincident signals, and of neuronal plasticity.

Animals↗
PubMedDate not supplied

L-deprenyl induces aromatic L-amino acid decarboxylase (AADC) mRNA in the rat substantia nigra and ventral tegmentum. An in situ hybridization study.

L-Deprenyl is a complex drug, and number of mechanisms have been proposed to explain its effects. These include blockade of dopamine metabolism, amplification of dopamine responses, induction of superoxide dismutase or delaying apoptosis. Using in situ hybridization techniques, we have shown that L-deprenyl (5-10 mg/kg intraperitoneally, killed after 24 h) increases aromatic L-amino acid decarboxylase (AADC) mRNA levels in rat substantia nigraventral tegmental area. In human brain tissue, AADC is present at low levels, suggesting a possible rate-limiting role in monoamine synthesis. This is particularly important in parkinsonian patients, since the therapeutic efficacy of L-DOPA is attributed to its enzymatic decarboxylation to dopamine. The present findings support that one of the effects of L-deprenyl may be to facilitate the decarboxylation of L-DOPA by increasing the availability of AADC.

Animals↗
PubMedDate not supplied

The encapsulation of a model protein in poly (D, L lactide-co-glycolide) microparticles of various sizes: an evaluation of process reproducibility.

Poly (D, L lactide-co-glycolide) and poly (D, L lactide) microparticles were prepared by solvent evaporation and the process reproducibility was evaluated in terms of the loading of a model protein into the microparticles, the microparticle size and the in-vitro release profiles of the protein. The results showed that the microencapsulation method allowed the preparation of microparticles with mean sizes from < 0.5 micron to 100 microns in size, with protein entrapment from 0.5 to 5% w/w. The microparticles were smooth and free from surface defects. Moreover, the reproducibility of the preparation method was demonstrated by the in-vitro release profiles obtained using different batches of microparticles prepared under similar conditions and by the reproducibility of microparticle size and protein loading. The results demonstrated that the preparation method was both robust and reproducible and allowed the preparation of microparticles with desired characteristics in terms of loading levels, particle size and release rates.

Lactic Acid↗
PubMedDate not supplied

Multiresidue gas chromatographic method for determining synthetic pyrethroid pesticides in agricultural products: collaborative study.

Fourteen laboratories from 6 countries and regions participated in an international collaborative study to evaluate a multiresidue gas chromatographic (GC) method for determining 8 synthetic pyrethroid pesticides in grains, fruits, and vegetables. The study design was based on Youden's matched-pairs principle for collaborative tests of analytical methods. Each laboratory analyzed 12 collaborative samples of wheat, oranges, and tomatoes as blind samples. Wheat samples were extracted with acetonitrile-water (2 + 1), while orange and tomato samples were extracted with acetone. Residues were partitioned into hexane, evaporated to dryness with a rotary evaporator, and then dissolved in hexane. The hexane extract was partitioned with acetonitrile and cleaned up on a 5% water-deactivated Florisil column with 6% ethyl ether in hexane as eluant. Residue concentrations were determined by GC with electron capture detection with splitless injection by comparison with single-point calibration standards. The appropriate standard concentration was determined by screening sample extracts before analysis. The multiresidue method was tested over the concentration range of 0.095-1.909 mg/kg depending on the 8 different of pesticides and agricultural products analyzed in the collaborative study. Statistical analysis of data from 13 laboratories showed weighted average recoveries for 8 pyrethroids in wheat, oranges, and tomatoes at 0.105-1.909, 0.095-1.909, and 0.105-0.954 mg/kg, respectively, ranging from 91.8 to 100.2%, from 88.1 to 100.6%, and from 88.2 to 101.5%, respectively. Reproducibility relative standard deviation values ranged from 6.46 to 17.74%, from 5.94 to 18.13%, and from 5.59 to 10.48%, respectively. Repeatability relative standard deviation values ranged from 6.34 to 10.84%, from 5.19 to 11.72%, and from 3.20 to 8.09%, respectively. The multiresidue GC method for determining synthetic pyrethroid pesticides in agricultural products has been adopted first action by AOAC INTERNATIONAL.

Chromatography, Gas↗
PubMedDate not supplied

Determination of clopidol residues in chicken tissues by liquid chromatography: part I. Optimization of analytical conditions and comparison with AOAC gas chromatography method.

A simple and specific liquid chromatographic method was developed for determination of clopidol in chicken tissues. Samples were extracted with acetonitrile. The extracts were cleaned up on an alumina column and an anion exchange column. The clopidol was separated on a column (30 cm x 3.9 mm) of microBondapak C18 (10 microm) by using acetonitrile-water (20 + 80, v/v) as mobile phase, and determined quantitatively at 270 nm. Recoveries were 86.0-97.6%, with relative standard deviations of 2.14-9.42% at 0.010-2.0 mg/kg from 4 spiked matrixes of chicken muscle, egg, liver, and kidney. The limit of detection was 0.005 mg/kg. Compared with the modified AOAC gas chromatographic method, the present method is simple and fast to operate. Its results are accurate and reliable, making it favorable for environmental protection and meeting requirements for human safety. Thus, it is suitable for routine analysis of large quantities of samples.

Animals↗