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Biomedical subjects

R Feng

Publications and source records attributed to R Feng.

At least 55 records · Page 3Linked to original sources
PubMed1992

Analysis of antibodies and other large glycoproteins in the mass range of 150,000-200,000 Da by electrospray ionization mass spectrometry.

The analytical applicability of electrospray ionization mass spectrometry (ESIMS) to large glycoproteins in the molecular weight (MW) range of 150,000-200,000 was demonstrated. Multiply charged ions (charge state as high as 150+) of several typical macrosized glycoproteins of immunological significance were generated by pneumatically-assisted electrospray (ionspray) and their masses measured on a quadrupole mass spectrometer having a mass-to-charge (m/z) range of 2400. The resolution of the quadrupole instrument was insufficient to resolve the glycocomposition microheterogeneities in the MW range studied. Nevertheless, the average MWs of three immunoglobulin G (IgG) class murine monoclonal antibodies, anti-(human alpha 1-antitrypsin) (148,484 +/- 4), anti-(human alpha 1-acid glycoprotein) (149,599 +/- 12) and anti-(beta-galactosidase) (component I, 150,544 +/- 10, and component II, 151,496 +/- 17), and human alpha 2-macroglobulin monomer (186,100 +/- 100), and human complement component C4 (196,863 +/- 29) were still determined from the fused peak profiles of their constituent glyco components (the errors given reflect the measurement precisions of the simultaneous multichannel MW determinations). The difference between the measured average MW and the unmodified sequence MW was used to assess the degree of post-transitional modification in human alpha 2-macroglobulin (13.6%) and human complement component C4 (5.3%). For the large glycoproteins studied here, glycosylation did not appear to seriously affect the effectiveness of the electrospray ionization; up to 70% of their full charge-retaining capacities were fulfilled under the usual experimental conditions. These results show that ESIMS is capable of providing analytically useful information for macrosized proteins.

Antibodies↗
PubMed1992

[Establishment and preliminary application of competitive ELISA using monoclonal antibody against Trichinella spiralis].

Monoclonal antibody competitive ELISA was devised with a highly specific McAb (2G8) against T. spiralis. Among 20 rabbits infected with T. spiralis experimentally. 35% (7/20) were positive on the 17th day post infection (PI); 100% positive on the 31st day PI. No cross reaction was found with 29 sera of rabbits infected with other kinds of helminth. The dynamic antibody titer of five infected rabbits sera were studied with this method. The change may be helpful to judge the state of infection. In short, anti-T. spiralis McAb competitive ELISA can be regarded as a sensitive and specific immunological diagnostic method for T. spiralis infection.

Animals↗
PubMed1992

[A method for acquiring newborn larvae of Trichinella spiralis in vitro].

This paper reports a simple method for acquiring numerous newborn larvae of Trichinella spiralis in vitro. Adults of T. spiralis, collected from small intestine on rats which were infected with infective larvae separated from mice infected experimentally, were put into tissue culture bottle containing M199. Then the bottles were incubated in CO2 incubator (37 degrees C, 5% CO2) for 15-20h. The newborn larvae were collected by passing through filtration, centrifugation and repeated wash. The results showed that this method is effective in terms of the activity of the adults and newborn larvae and the amount of larvae gained. The method in economical and can control bacterial contamination to a certain extent and extract ES antigen of adults and newborn larvae from the culture solution.

Animals↗
PubMed1992

[Chemical constituents of Drynaria propinqua (Wall) J. Sm].

Four compounds isolated from the rhizomes of Drynaria propinqua collected in Sichuan have been identified. One of them was a new natural product, namely propinqualin, whose structure was established as (-)-epiafzelechin-3-O-beta-D-allopyranoside. The other three were 4-O-beta-D-glucopyranosyl caffeic acid, beta-sitosterol-3-O-beta-D-glucopyranoside and sucrose.

Caffeic Acids↗
PubMed1992

[Chemistry and immunochemistry analysis of the soluble antigens of newborn larvae of Trichinella spiralis].

The soluble antigens of newborn larvae of Trichinella spiralis were characterized in terms of molecular weight of protein, glycoprotein and lipoprotein contents, and immunochemistry. After the antigens were separated with SDS-PAGE and then followed by ultrasensitive silver staining, at least 40 bands of proteins were noted. Correspondingly, 28 bands of glycoproteins and 9 bands of lipoproteins were revealed as the similar gels were stained by the hypersensitive periodic acid silver and Nile's blue staining respectively. Six specific bands were recognized using polyclonal antibodies in the serum of rabbits immunized with antigens of newborn larvae by immunoblotting. All of them are glycoproteins. The components of the antigens with molecular weight (MW) 41.5 kd, 40 kd, 29.5 kd, 25 kd, 11 kd and 18 kd were found to be species specific and newborn larva stage-specific target antigen relevantly.

Animals↗
PubMed1992

Mechanistic and structural studies on Rhodococcus ATCC 39484 nitrilase.

Rhodococcus ATCC 39484 produced a nitrilase when induced with isovaleronitrile. The enzyme was obtainable pure in milligram amounts, had a subunit Mr of 40 kDa, and demonstrated a substrate-induced activation related to aggregation of subunits to form a 560-kDa complex. The enzyme had a broad substrate specificity, had a pH optimum of 7.5, was stable up to 40 degrees C, and had one disulfide bridge and two free cysteine residues, one of which appeared to be catalytically essential. The N-terminal sequence was determined and found to have 78.3% homology, in a 23-residue overlap, with Klebsiella ozaenae nitrilase. The enzyme was inhibited competitively by benzylamine and benzaldehyde and irreversibly by benzyl bromide. However, benzyl bromide was shown to be nonspecific, causing multiple alkylation. Acid quenching of enzyme-substrate mixtures allowed for the detection of covalent enzyme-substrate complexes using mass spectrometry. The covalent intermediate is suggested to be either a thioimidate or an acylenzyme and a reaction mechanism consistent with this observation and also the inhibitor results is proposed. The rate of breakdown of the covalent intermediates was found to be rate limiting even for substrates with undetectable rates of hydrolysis or those with very slow rates of intermediate formation. For phenylacetonitrile, a poor substrate, in addition to acid, approximately 2% of the product was the corresponding amide. This result suggests that a tetrahedral intermediate is formed which, for selected substrates, can break down anomalously to produce amide in place of the normal acid product. Under the conditions used in this study all other substrates tested were converted to acid.

Amino Acid Sequence↗
PubMed1992

[Selective long-range DEPT NMR technique and its application to structural study of glycoside].

This paper reports a new NMR technique: selective long-range DEPT. The result obtained showed that the technique can be used to assign NMR signal of 13C, 15N and 31P nuclei, and connect the spin systems separated by quaternary carbon or heteroatom. This paper deals mainly with applying the technique for determining the glycosidation position in aglycone moiety and sequence of sugar moiety in a natural glycoside.

Glycosides↗
PubMed1991

Nature of papain products resulting from inactivation by a peptidyl O-acyl hydroxamate.

Mass spectrometry has been used to provide insights into the mechanism of inhibition of cysteine proteases by a hydroxylamine derivative, CBZ-Phe-Gly-NH-O-CO-(2,4,6-Me3)Ph. An oxidized form of papain resulting from the incubation of the enzyme with the peptidyl hydroxamate in the absence of a reducing agent has been identified as a sulfinic acid. The presence of a covalent enzyme-inhibitor complex of molecular mass consistent with a sulfenamide adduct of papain could also be detected by this method. Implications on the mechanism of inactivation of cysteine proteases by peptidyl hydroxamates are discussed.

Dithiothreitol↗
PubMed1991

[The structure of versicolactone A from Aristolochia versicolar S.M. Hwang].

A novel sesquiterpene lactone, versicolactone A, with 12-carbon ring skeleton, was isolated from the roots of Aristolochia versicolar S. M. Hwang. Versicolactone A, C15H20O2, colorless prisms, mp 130-132 degrees C, [alpha]6D +486 degrees (c 0.1276, CHCl3). Its structure was established by spectroscopic methods, mainly 2D-NMR (1H-1H COSY, 1H-13C COSY, COLOC), HRMS and metastable ion measurement.

Antineoplastic Agents, Phytogenic↗
PubMed1991

Analysis and pyrolysis of some N-nitrosamino acids in tobacco and tobacco smoke.

A new tobacco-specific nitrosamine, 4-(N-nitrosomethylamino)-4-(3-pyridyl)butyric acid (iso-NNAC), has been identified in tobacco, and its structure was confirmed by gas chromatography-mass spectrometry following enrichment of a tobacco extract. The levels of iso-NNAC ranged from 0.01 to 0.95 ppm. It does not induce DNA repair in primary rat hepatocytes and is inactive as a tumorigenic agent in strain A mice. In order to study the fate of nitrosamino acids during smoking, we spiked cigarettes with the following N-nitrosamino acids: iso-NNAC, 3-(nitrosomethylamino)propionic acid (NMPA), 4-(nitrosomethylamino)butyric acid (NMBA), N-nitrososarcosine (NSAR) and N-nitrosoproline (NPRO). NMPA and NMBA were partially transferred, unchanged, during smoking and partially formed the corresponding methyl esters, while pyrolysis of NSAR and NPRO resulted mainly in their decarboxylating products. This is the first time that the pyrosynthesis of methyl esters has been observed during smoking.

Animals↗
PubMed1990

Detection of covalent enzyme-substrate complexes of nitrilase by ion-spray mass spectroscopy.

Nitrilase from Rhodococcus ATCC 39484 was found to consist of two species of Mr 40,258 +/- 2 and 40,388 +/- 2 Da. When the enzyme was incubated with nitrile substrates and the reaction quenched with acid, higher Mr species were observed. The mass differences were consistent with addition of a substrate molecule to each species. These results represent the first reported demonstration that this, or any other nitrilase forms a covalent intermediate with its substrates. The observation that the intermediate, suggested to be either a thioimidate or an acylenzyme, can be trapped by acidification indicates that the rate of breakdown of the intermediate is rate-limiting.

Aminohydrolases↗
PubMed1990

[Preparation of monoclonal antibodies against Trichinella spiralis and localization of antigens].

BALB/c mice were infected per os with the infective larvae (L1) of Trichinella spiralis, and challenged by injecting 0.2ml soluble L1 antigen 3 days before cell fusion. SP2/0 myeloma and immune spleen cells were fused at the ratio of 1:5 in the presence 30%PEG (MW 4,000). The fusion rate and antibody positive rate were 92.1% and 16.6% respectively using ELISA. Among these the chromosomes of 4 strains were 2n greater than 100 and that of the SP2/0 myeloma cells 2n less than or equal to 70. The titer of McAb in the ascites was found to be 1/640 or 1/1,280. Eight strains were of IgG1, 1 IgG2a and 3 IgM in an agar system. Three strains of McAbs, which could recognize specifically the L1 antigen fractions by immuno-blotting technique, were used as probes to localize the target antigens in sections of T. spiralis L1. Staining was performed using an indirect technique consisting of goat anti-mouse IgG-conjugated horseradish peroxidase on de-paraffin sections, and substrate DAB. The results revealed that the antigens reacted most strongly with the specific McAbs were located in the cuticle and stichosome, followed by the lining of gut. Among the 3 strains of McAbs used, 2E5F11A5 reacted most strongly with the antigen, followed by 2E5E9E4. 2E5E9G5 was the weakest.

Animals↗
PubMed1989

[The structure of versicolactone D].

The extracts of Aristolochia versicolar S.M. Huang root afforded a new dimeric sesquiterpene lactone, versicolactone D, with a novel skeleton. Its structure was established by spectroscopic methods, mainly X-ray and 2D-NMR.

Chemical Phenomena↗
PubMed1989

[1H, 13C NMR and stereochemistry studies of 3S-substituted alkoxylquinuclidine by two-dimensional and NOE difference NMR techniques].

By using optically pure 3S-quinuclidinol, two diastereoisomers (3S-1) and (3S-2) of 3-(substituted) alkoxy-quinuclidine were synthesized. 1H and 13C NMR spectra of (3S-1) and (3S-2) have been completely analyzed utilizing double-quantum filtered COSY, 13C-1H COSY and NOE difference experiment. The NOE difference experiment was used to determine the absolute configuration at C-11 of the diastereomers. According to the results of NOE difference and variable concentration NMR experiments, the configuration about C-11 of (3S-1) is designated as R (1A), whereas the configuration about C-11 of (3S-2) is designated as S (1B). The result was confirmed by X-ray diffraction analysis.

Magnetic Resonance Spectroscopy↗
PubMed1988

Ultrasonic attenuation in red blood cell suspensions.

A theoretical analysis of ultrasonic attenuation in aqueous suspensions of red blood cells was carried out. This verified the relative importance of several mechanisms: absorption accounts for 60% of the attenuation, viscous relative motion loss accounts for less than 30%, and the sound scattering contribution is negligible.

Erythrocytes↗