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Biomedical subjects

B Shen

Publications and source records attributed to B Shen.

At least 181 records · Page 10Linked to original sources

Calcium alginate immobilized hybridomas grown using a fluidized-bed perfusion system with a protein-free medium.

Hybridoma SPO1 cells were immobilized in calcium alginate beads and were further grown in a fluidized-bed perfusion system with a protein-free medium. The presence of serum in the steps of entrapment was shown to be helpful for the preservation of cell viability. Each step during immobilization was investigated with respect to the extent of cell damage caused. The immobilization process using small beads caused a lower cell viability initially but allowed a higher rate of cell growth subsequently, compared to those in large beads. In a perfusion system for the continuous production of monoclonal antibodies (MAb), the viable cell density reached 2 x 10(7) cells per ml of beads with a viability of 40%. Compared with the cells in suspension culture, the immobilized SPO1 cells showed higher viable cell based specific rates of substrate uptake (glucose and glutamine) and of MAb production. A significant drop in the formation of lactate after the cell growth entered a steady state suggested a higher activity of the Tricarboxylic Acid Cycle in the cells when the cell density became high.

Alginates↗

The enhancer-blocking suppressor of Hairy-wing zinc finger protein of Drosophila melanogaster alters DNA structure.

Insertion of the gypsy retrotransposon of Drosophila melanogaster into a gene control region can repress gene expression. The zinc finger protein (SUHW) encoded by the suppressor of Hairy-wing [su(Hw)] gene binds to gypsy and prevents gene enhancers from activating transcription. SUHW blocks an enhancer only when positioned between the enhancer and promoter. Although position dependent, SUHW enhancer blocking is distance independent. These properties indicate that SUHW does not interact with the transcription activator proteins that bind to enhancers. To explore if DNA distortions are involved in enhancer blocking, the ability of SUHW to alter DNA structure was examined in gel mobility assays. Indeed, SUHW induces an unusual change in the structure of the binding-site DNA. The change is not a directed DNA bend but correlates with loss of sequence-directed bends in the unbound DNA. The DNA distortion requires a SUHW protein domain not required for DNA binding, and mutant proteins that fail to alter DNA structure also fail to eliminate the sequence-directed bends. These results suggest that SUHW increases DNA flexibility. The DNA distortion is not sufficient to block enhancers, and therefore it is suggested that increased DNA flexibility may help SUHW interact and interfere with proteins that support long-distance enhancer-promoter interactions.

Animals↗

[A study of the distribution of PGM1 subtypes in fifteen nationalities in Yunnan Province China].

A study of the distribution of PGM1 subtypes in the fifteen nationalities in Yunnan province in China, including Han, Yi, Bai, Kucong, Hani, Dai, Yao, Jino, Blang, Wa, Lahu, Hui, Lisu Naxi and Pumi, was carried out, using ultrathin-layer polyacrylamide gel isoelectric focusing (ULPAGIEF). Gene frequencies and probabilities of discrimination (DP) of PGM1 subtypes in these nationalities were calculated. Statistical tests show: That there is a clear nationalistic discrepancy in the fifteen nationalities; but there is not an areal discrepancy in the Han nationality, living in different areas, on the distribution of PGM1 subtypes. The result of the study also shows, that there are high probabilities of discrimination for PGM1 subtypes in all fifteen nationalities.

China↗

Azotobacter vinelandii ferredoxin I. Aspartate 15 facilitates proton transfer to the reduced [3Fe-4S] cluster.

The [3Fe-4S]+/0 cluster of Azotobacter vinelandii ferredoxin I (AvFdI) has an unusually low and strongly pH-dependent reduction potential (E'0). The reduced cluster exists in two forms, depending upon pH, that exhibit substantially different magnetic circular dichroism (MCD) spectra. Recent studies have established that the MCD changes observed on decreasing the pH from 8.3 (alkaline form) to 6.0 (acid form) cannot be explained either by a change in spin state of the cluster (Stephens, P.J., Jensen, G.M., Devlin, F.J., Morgan, T.V., Stout, C. D., Martin, A.E., and Burgess, B.K. (1991) Biochemistry 30, 3200-3209) or by a major structural change (e.g. ligand exchange) (Stout, C.D. (1993) J. Biol. Chem. 268, 25920-25927). Here, we have examined the influence of aspartate 15 on the pH dependence of the spectroscopic and electrochemical properties of AvFdI by construction of a D15N mutant. Aspartate 15, which is salt-bridged to lysine 84 at the protein surface, is the closest ionizable residue to the [3Fe-4S] cluster. The results show that replacement of aspartate by asparagine results in an approximately 20-mV increase in E'0 for the [3Fe-4S]+/0 cluster at high pH concomitant with an approximately 0.8-pH unit decrease in the pK of the reduced form. The major pH dependence of E'0 is preserved as is the effect observed by MCD. These data eliminate the possibility that the MCD change is due to the presence of Asp-15 and support the conclusion that it originates in direct protonation of the [3Fe-4S]0 cluster, probably on a sulfide ion. Voltammetric studies show that interconversion between [3Fe-4S]+ and [3Fe-4S]0 at acidic pH involves rapid electron transfer followed by proton transfer (for reduction) and then proton transfer followed by electron transfer (for oxidation). Ionized aspartate 15 facilitates proton transfer. Thus, protonation and deprotonation are much slower for D15N relative to the native protein at pH > 5.5. Proton transfer reactions necessary for further reduction of the [3Fe-4S]0 cluster to the [3Fe-4S]- and [3Fe-4S]2- states are also retarded in D15N. The results suggest that the carboxylate-ammonium salt bridge afforded by Asp-15-Lys-84 conducts protons between the cluster and solvent H2O molecules. Overproduction of D15N FdI, but not native FdI, in A. vinelandii has a negative effect on the growth rate of the organism, suggesting that the rate of protonation or deprotonation of the [3Fe-4S]0 cluster may be important in vivo.

Amino Acid Sequence↗

Enzymatic synthesis of a bacterial polyketide from acetyl and malonyl coenzyme A.

Microorganisms and plants manufacture a large collection of medically and commercially useful natural products called polyketides by a process that resembles fatty acid biosynthesis. Genetically engineered microorganisms with modified polyketide synthase (PKS) genes can produce new metabolites that may have new or improved pharmacological activity. A potentially general method to prepare cell-free systems for studying bacterial type II PKS enzymes has been developed that facilitates the purification and reconstitution of their constituent proteins. Selective expression of different combinations of the Streptomyces glaucescens tetracenomycin (Tcm) tcmJKLMN genes in a tcmGHIJKLMNO null background has been used to show that the Tcm PKS consists of at least the TcmKLMN proteins. Addition of the TcmJ protein to the latter four enzymes resulted in a greater than fourfold increase of overall activity and thus represents the optimal Tcm PKS. Polyclonal antibodies raised against each of the TcmKLMN proteins strongly inhibit the Tcm PKS, as do known inhibitors targeted to the active site Cys and Ser residues of a fatty acid synthase. This system exhibits a strict starter unit specificity because neither propionyl, butyryl, or isobutyryl coenzyme A substitute for acetyl coenzyme A in assembly of the Tcm decaketide. Because the Tcm PKS activity is significantly diminished by removal of the TcmM acyl carrier protein and can be restored by addition of separately purified TcmM to two different types of TcmM-deficient PKS, it should be possible to use such preparations to assay for each of the constituents of the Tcm PKS.

Acetyl Coenzyme A↗

Tetracenomycin F2 cyclase: intramolecular aldol condensation in the biosynthesis of tetracenomycin C in Streptomyces glaucescens.

Tetracenomycin (Tcm) F2 cyclase, which catalyzes the cyclization of the anthrone Tcm F2 to the naphthacenone Tcm F1 in the biosynthesis of the anthracycline antibiotic Tcm C in Streptomyces glaucescens, has been purified to homogeneity and characterized. The N-terminal sequence of the enzyme establishes that it is encoded by the tcmI gene, whose deduced product has a molecular weight of 12,728. SDS-PAGE analysis gave a single band with a molecular weight of 12,500, whereas gel-filtration chromatography yielded a molecular weight of 37,500, indicating that the Tcm F2 cyclase is a homotrimer in solution. Under pH > or = 8.0, the enzyme catalyzes the cyclization of Tcm F2 to Tcm F1 and has a Km of 121 +/- 18.2 microM and Vmax of 704 +/- 62.3 nmol.min-1.mg-1. In contrast, under pH < or = 6.5, it catalyzes the cyclization of Tcm F2 to 9-decarboxy Tcm F1, a known shunt metabolite of the Tcm C biosynthetic pathway. Tcm F2 cyclase represents the first discrete enzyme for carbon-carbon bond formation via an intramolecular aldol condensation-dehydration mechanism, a key biochemical operation proposed in the early steps of the biosynthesis of all aromatic polyketides.

Aldehyde-Lyases↗

Mutagenesis of structural half-cystine residues in human thioredoxin and effects on the regulation of activity by selenodiglutathione.

A human thioredoxin cDNA was modified to optimize Escherichia coli expression and subcloned into the plasmid pACA, a vector for T7 RNA polymerase-directed expression. The substitution of structural (noncatalytic) half-cystines in human thioredoxin (hTrx) was made by site-directed mutagenesis. The recombinant wild-type (wt) hTrx and its mutant C61S, C72S, and C61S/C72S were expressed and purified to homogeneity. Characterization of the wt and mutant hTrx was done with respect to redox activity with thioredoxin reductase (TR), tryptophan fluorescence, and effects of incubation with GS-Se-SG, which is believed to be the major metabolite of inorganic selenium compounds in mammalian tissues. The Km and kcat of wild-type hTrx for human placenta thioredoxin reductase (HP-TR) at pH 7.0 were 2.0 microM and 2800 min-1, respectively. The mutant proteins C61S, C72S, and C61S/C72S had Km and kcat values similar to those of the wt thioredoxin. Tryptophan fluorescence measurements showed that the wt and mutant proteins had similar stability to a denaturing agent. Incubation of fully reduced thioredoxin with 0.1 molar equivalent of GS-Se-SG resulted in continued oxidation of SH groups. After 3.5 h only 0.5 of initially 4.6 SH groups/thioredoxin remained. With the oxidized protein, a pronounced lag phase in thioredoxin reductase-dependent insulin disulfide reduction was present. Disulfide-linked dimers of the protein were present. The results clearly showed that noncatalytic cysteine residues in hTrx were oxidized accompanied by dimerization and inactivation. The activities of the mutant proteins C72S and C61S/C72S were unchanged after 3 h of incubation with GS-Se-SG. No dimer appeared of the C72S thioredoxin.(ABSTRACT TRUNCATED AT 250 WORDS)

Amino Acid Sequence↗

Tetracenomycin F1 monooxygenase: oxidation of a naphthacenone to a naphthacenequinone in the biosynthesis of tetracenomycin C in Streptomyces glaucescens.

Tetracenomycin (Tcm) F1 monooxygenase, which catalyzes the oxidation of the naphthacenone Tcm F1 to the 5,12-naphthacenequinone Tcm D3 in the biosynthesis of the anthracycline antibiotic Tcm C in Streptomyces glaucescens, has been purified to homogeneity and characterized. Gel filtration chromatography yields a molecular weight of 37,500 whereas SDS-PAGE gives a single band with a molecular weight of 12,500, indicating that the Tcm F1 monooxygenase is a homotrimer in solution. The N-terminal sequence of the enzyme establishes that it is encoded by the tcmH gene. The monooxygenase displays an optimal pH of 7.5 and has a Km of 7.47 +/- 0.67 microM and Vmax of 473 +/- 10 nmol.min-1.mg-1. Formally, the Tcm F1 monooxygenase can be classified as an internal monooxygenase that requires only O2 for the enzymatic oxidation. Yet, it apparently does not possess any of the prosthetic groups of known monooxygenases, such as flavin or heme groups, nor does it utilize metal ions. It is inactivated by p-chloromercuribenzoic acid, N-ethylmaleimide, and diethyl pyrocarbonate, suggesting that sulfhydryl groups and histidine residues are essential for the enzyme activity.

Anti-Bacterial Agents↗

Chronic lymphocytic leukemia with low lymphocyte count.

BACKGROUND: A peripheral blood absolute lymphocyte count (ALC) of greater than 5 x 10(9)/l is considered the required minimum for diagnosis of chronic lymphocytic leukemia (CLL). Cases with low ALC (CLL-LLC), less than 5 x 10(9)/l, have not been included in the current staging systems, and would not be suspected of having CLL, or investigated for the disease, especially in the absence of clinical manifestations. On the other hand, the diagnostic value of the differential lymphocyte counts have not been emphasized. METHODS: Cell suspensions from peripheral blood of previously untreated cases of CLL-LLC (n = 12) and typical CLL (n = 189) were analyzed for immunologic evaluation of surface immunoglobulin (SIg), mouse erythrocyte rosettes, CD5, CD19, CD20, CD22, and CD2, as well as cytochemical evaluation of tartrate-resistant acid phosphatase (TRAP). The results in CLL-LLC were compared statistically with typical CLL. RESULTS: The ages of the 12 patients with CLL-LLC ranged from 47 to 84 years. The absolute lymphocyte counts ranged from 1.5 x 10(9)/l to 4.9 x 10(9)/l, and the percentage of lymphocytes in the differential leukocyte counts ranged from 52% to 93%. None of the patients had signs and symptoms of CLL or other conditions that may cause reactive lymphocytosis. CLL-LLC demonstrated similar characteristics to typical CLL, i.e., weak expression of monoclonal SIg, mouse rosette formation, positive CD5, high CD19 and CD20, negative CD22 and TRAP. No statistical differences existed between the immunologic markers or between SIg isotype distribution in the two groups. CONCLUSIONS: Cases of CLL-LLC constituted 6% of B-CLL and would have been missed if immunologic investigation was not carried out because of the absence of absolute lymphocytosis and clinical manifestations of CLL. Persistent relative lymphocytosis of > or = 50% of the differential leukocyte count in older individuals (older than 50 years of age), is an indication for further investigation of CLL by immunophenotyping of peripheral blood lymphocytes and examination of bone marrow.

Aged↗

Diagnostic value of clonality of surface immunoglobulin light and heavy chains in malignant lymphoproliferative disorders.

Cell suspensions from the peripheral blood of B-chronic lymphoid leukemias (B-CLL, n = 274) and reactive lymphocytosis (RLC, n = 132) and from solid tissue samples of B-non-Hodgkin's lymphoma (B-NHL, n = 466) and reactive lymphadenopathy (RLA, n = 324) were analyzed to evaluate the diagnostic value of clonality of L- and H- chains in B-CLL and B-NHL. Cutoff levels for monoclonal L-chain (mono-L) and monoclonal H-chain (mono-H) were defined. In B-CLL, the association patterns of L- and H- chains were as follows: mono-L/mono-H, 245 cases (89.42%); mono-L/polyclonal H chain (poly-H), 4 (1.46%); polyclonal L chain (poly-L)/mono-H, 2 (0.73%); poly-L/poly-H, 2 (0.73%); undetected (und)-L/mono-H, 6 (2.19%); and und-L/und-H, 15 (5.47%). In B-NHL, the association patterns were mono-L/mono-H, 433 cases (92.92%); mono-L/poly-H, 4 (0.86%); poly-L/mono-H, 8 (1.72%); poly-L/poly-H, 2 (0.43%); und-L/mono-H, 4 (0.86%); and und-L/und-H, 15 (3.22%). Monoclonality of H chains are complementary to L-chain restriction, especially in the cases with poly-L or und-L, and should be considered as a positive criterion in determining surface immunoglobulin (SIg) clonality. Monoclonality of SIg assessed by both L and H chains is both sensitive and specific for the diagnosis of B-CLL and B-NHL, and their differentiation from RLC and RLA, since none of the cases of RLC and RLA showed monoclonal SIg.

Cloning, Molecular↗

Long-term potentiation in hippocampal CA1: effects of afterdischarges, NMDA antagonists, and anticonvulsants.

Long-term potentiation (LTP) of the basal dendritic population excitatory postsynaptic potential (EPSP) in hippocampal CA1 was readily elicited in behaving rats, without afterdischarges (ADs), by theta-frequency-patterned primed bursts (PBs) delivered to the contralateral CA1. A long-lasting postictal potentiation (PIP) was also elicited by high-frequency trains (1 s at 200 Hz), following an AD and a 5- to 10-min depression. The N-methyl-D-aspartate (NMDA) antagonist 2-amino-phosphonovalerate was effective in blocking both LTP and PIP. The noncompetitive NMDA antagonist MK801 (0.5 mg/kg ip) attenuated the PB-induced LTP but enhanced PIP. The anticonvulsants phenytoin (40 mg/kg ip) and U54494A (25 or 50 mg/kg ip) had no effects on the LTP induced by a PB but they, like MK801, enhanced PIP to various degrees. The apparent enhancement of PIP by anticonvulsants may be a direct result of shortening the hippocampal AD duration and alleviation of the postictal EPSP depression. It is inferred that the typical hippocampal AD did not induce potentiation, but rather a postictal depression of the EPSP or a suppression of LTP. The mechanism of the postictal depression is likely different from the NMDA receptor-mediated LTP and PIP and it may depend on the AD duration (and perhaps excessive CA2+ influx) but not critically on NMDA receptors.

2-Amino-5-phosphonovalerate↗

Influence of selenium on the microvasculature of the retina.

The impact of small differences in selenium exposure during the first year of life was investigated in male Wistar rats. Forty-five rats were evaluated in two experiments. Rats were provided diets that contained sucrose as the sole carbohydrate to induce an elevation in blood triglycerides, cholesterol, glucose, and insulin. In each experiment one-half the rats received 0.1 mg Se/kg and the other half 0.2 mg Se/kg diet. Both levels of selenium supported normal activity of the marker for selenium sufficiency erythrocyte glutathione peroxidase. In experiment 1 rats were maintained in galvanized cages and in experiment 2 they were housed in stainless steel cages. In both experiments rats provided 0.2 mg Se/kg diet had fewer acellular degenerating capillaries and a higher ratio of pericyte to endothelial cells in the capillary wall than those fed 0.1 mg/kg as well as fewer vessels over the optic disc head. In the second experiment, the height of the central choroid was also greater in rats exposed to the higher level of selenium suggesting that the element protected the capillaries in this region from degeneration. In contrast to vascular tissue, the retinal parenchymal tissue was unaffected by the level of selenium exposure. These results are consistent with the hypothesis that the microvasculature has a unique requirement for selenium.

Animals↗

Isolation and structural elucidation of tetracenomycin F2 and tetracenomycin F1: early intermediates in the biosynthesis of tetracenomycin C in Streptomyces glaucescens.

This report describes the fermentation, isolation, and structural elucidation of tetracenomycin (Tcm) F2 [2], a metabolite produced by a blocked mutant strain WMH1092 of the Tcm C [1] producer Streptomyces glaucescens and by the recombinant strain S. glaucescens WMH1077 (pWHM722). Elucidation of the Tcm F2 structure shows that 2 is the earliest intermediate identified to date in the biosynthesis of 1. This is supported by the fact that 2 is very efficiently biotransformed to 1 by the S. glaucescens WMH1068 strain and is enzymatically converted to Tcm F1 [3] and to Tcm D3 [4], a known intermediate of Tcm C biosynthesis.

Anthracenes↗

Combined assay of surface immunoglobulin intensity and mouse rosettes. A practical parameter in the differential diagnosis of small lymphocytic and follicular center cell lymphomas.

Cell suspensions from the lymph nodes of small lymphocytic lymphoma (n = 94) and nodular and diffuse follicular center cell lymphomas (n = 330) were analyzed to evaluate the diagnostic significance of the surface immunoglobulin (SIg) intensity and mouse rosette assay (MR). In small lymphocytic lymphoma, SIg was monoclonal in 65 cases (69.15%), with weak fluorescence in 59 (90.77%). It was not detected in 29 cases (30.85%). The MR findings were positive in 68 cases (72.34%) and negative in 26 (27.66%). The combined results of these two assays showed the following: weak SIg/MR+, 35 (37.23%); weak SIg/MR-, 24 (25.53%); strong SIg/MR+, 6 (6.38%); strong SIg/MR-, 0; undetected SIg/MR+, 27 (28.72%); and undetected SIg/MR-, 2 (2.13%). By performing the assays for these two markers and accepting weak SIg/MR+, weak SIg/MR-, strong SIg/MR+, or undetected SIg/MR+ as sufficient for diagnosis, 92 cases (97.87%) were diagnosed. In diffuse follicular center cell lymphomas, SIg was monoclonal in 287 cases (86.97%), with strong fluorescence in 258 (89.9%) and weak fluorescence in 29 (10.1%). It was not detected in 43 cases (13.03%). The MR results were positive in 34 cases (10.3%) and negative in 296 (89.7%). The combined findings of these two assays showed that strong SIg/MR- was present in 244 cases (73.94%). The diagnostic value of the combined assay in the differential diagnosis between small lymphocytic lymphoma and diffuse follicular center cell lymphomas was proved using five statistical parameters.

Animals↗

The Drosophila melanogaster suppressor of Hairy-wing zinc finger protein has minimal effects on gene expression in Saccharomyces cerevisiae.

Many mutations in Drosophila melanogaster are gypsy retrotransposon insertions. Gypsy binds the protein (SUHW) encoded by the suppressor of Hairy-wing [su(Hw)] gene, and SUHW alters expression of surrounding genes. When gypsy is between an enhancer and promoter, SUHW blocks activation of transcription by the enhancer. Additionally, when gypsy is downstream of a promoter in a parallel orientation, SUHW increases truncation of transcripts at the poly(A) site in the gypsy 5' long terminal repeat, thereby decreasing the gene transcript levels. The effects of SUHW appear to involve fundamental and general mechanisms controlling gene expression because SUHW potentiates other poly(A) sites and blocks several enhancers in Drosophila. To investigate these mechanisms, SUHW was expressed in Saccharomyces cerevisiae. Although SUHW enters the nucleus and binds DNA in yeast, it has surprisingly minor effects on utilization of the CYC1 poly(A) site and transcription activation by a GAL upstream activation sequence. These observations indicate that the observed effects of SUHW on gene expression in Drosophila require specific interactions with other factors that are absent or unrecognizable in yeast.

Animals↗

Azotobacter vinelandii mutS: nucleotide sequence and mutant analysis.

An Azotobacter vinelandii homolog to the Salmonella typhimurium mutS gene was discovered upstream of the fdxA gene. The product of this gene is much more similar to S. typhimurium MutS than either is to the HexA protein of Streptococcus pneumoniae. An A. vinelandii delta mutS mutant strain was shown to have a spontaneous mutation frequency 65-fold greater than that of the wild type.

Adenosine Triphosphatases↗

Immunophenotyping of subtypes of B-chronic (mature) lymphoid leukemia. A study of 242 cases.

BACKGROUND: The French-American-British group's proposal for the classification of chronic lymphoid leukemias is unique at this time. Testing, expanding, and adding to the theory by immunophenotyping will help to additionally characterize this group of diseases. METHODS: Peripheral blood samples from 242 patients with chronic lymphoid leukemias were analyzed for immunologic evaluation of the following subtypes: typical chronic lymphocytic leukemia (CLL), 189; CLL with pleomorphic lymphocytes (CLL-pleo), 19; CLL of mixed cell type (CLL/PL), 20; prolymphocytic leukemia (PLL), 22; hairy cell leukemia (HCL), 10; HCL-variant, 1; and splenic lymphoma with villous lymphocytes, 1. RESULTS: The phenotype of CLL and CLL-pleo was weak surface immunoglobulin (SIg) with positive results of mouse rosettes (MR+), CD5+, and CD22-. Of PLL and HCL, it was strong SIg, MR-, CD5-, and CD22+. By analyzing the four markers and accepting the relevant results of two or more as sufficient for diagnosis, all cases (100%) of CLL, CLL-pleo, PLL, and HCL were diagnosed. CLL/PL showed the phenotype of CLL in 66.67% and of PLL in 33.33% of patients. The frequency of cases with weak fluorescence in decreasing order was CLL, CLL-pleo, CLL/PL, and PLL and HCL. The same sequence applied to the mean percentage of mouse rosette-forming cells and CD5 cells, but the sequence was reversed for CD22 cells. CONCLUSIONS: SIg intensity, MR, CD5, and CD22 constitute the minimum number of immune markers for the differential diagnosis of the subtypes of chronic lymphoid leukemia. The frequency of the four markers among the subtypes suggested that CLL and CLL-pleo have identical phenotypes and that the five subtypes follow a continuous range of B-cell differentiation from early mature (CLL and CLL-pleo) to late mature pre-plasma cell stages (PLL followed by HCL), with CLL/PL of intermediate maturity.

Adult↗