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Biomedical subjects

J Feng

Publications and source records attributed to J Feng.

At least 253 records · Page 14Linked to original sources
PubMed1995

Activation of transcription initiation from the nac promoter of Klebsiella aerogenes.

The nac gene of Klebsiella aerogenes encodes a bifunctional transcription factor that activates or represses the expression of several operons under conditions of nitrogen limitation. In experiments with purified components, transcription from the nac promoter was initiated by sigma 54 RNA polymerase and was activated by the phosphorylated form of nitrogen regulator I (NRI) (NtrC). The activation of the nac promoter required a higher concentration of NRI approximately P than did the activation of the Escherichia coli glnAp2 promoter, and both the promoter and upstream enhancer element contributed to this difference. The nac promoter had a lower affinity for sigma 54 RNA polymerase than did glnAp2, and uninitiated competitor-resistant transcription complexes formed at the nac promoter decayed to competitor-sensitive complexes at a greater rate than did similar complexes formed at the glnAp2 promoter. The nac enhancer, consisting of a single high-affinity NRI-binding site and an adjacent site with low affinity for NRI, was less efficient in stimulating transcription than was the glnA enhancer, which consists of two adjacent high-affinity NRI-binding sites. When these binding sites were exchanged, transcription from the nac promoter was increased and transcription from the glnAp2 promoter was decreased at low concentrations of NRI approximately P. Another indication of the difference in the efficiency of these enhancers is that although activation of a nac promoter construct containing the glnA enhancer was relatively insensitive to subtle alterations in the position of these sites relative to the position of the promoter, activation of the natural nac promoter or a nac promoter construct containing only a single high-affinity NRI approximately P binding site was strongly affected by subtle alterations in the position of the NRI approximately P binding site(s), indicating a face-of-the-helix dependency for activation.

Bacterial Proteins↗
PubMed1995

Repression of the Klebsiella aerogenes nac promoter.

Transcription of the nitrogen-regulated nac promoter of Klebsiella aerogenes requires sigma54 RNA polymerase, is activated by the phosphorylated form of the transcription factor nitrogen regulator I (NRI) (NtrC), and is repressed by the product of the nac gene, Nac. Nac protects a large portion of the nac control region, extending from positions -130 to -70, from digestion by DNase I. This site(s) lies immediately upstream from the site at which sigma 54 RNA polymerase binds, is downstream of a high-affinity binding site for the transcriptional activator NRI approximately P, and partially overlaps a low-affinity NRI approximately P-binding site. Binding of Nac to the DNA resulted in bending of the DNA but did not interfere with the binding of sigma 54 RNA polymerase to the promoter or with the binding of NRI approximately P to either the high-affinity site or low-affinity site. Furthermore, transcription assays with various wild-type and mutant templates suggested that Nac did not exclude NRI approximately P from either the low- or high-affinity sites, nor did Nac interfere with the ability of the polymerase to form the open complex when the binding sites for NRI approximately P were moved to different locations upstream from the promoter. Rather, Nac seemed to repress by an antiactivation mechanism in which the interaction of the NRI approximately P, bound at its normal sites, with sigma 54 RNA polymerase, bound to the promoter, was prevented.

Bacterial Proteins↗
PubMed1995

Role of chloride currents in repolarizing rabbit atrial myocytes.

Rabbit atrial cells manifest a prominent transient outward K+ current (Ito1), but this current recovers slowly from inactivation and is unlikely to be important at physiological rates (3-5 Hz). Depolarization of rabbit atrial cells also elicits a transient Ca(2+)-dependent outward Cl- current (Ito2). To compare the relative magnitude of these transient outward currents at various rates, we applied whole cell voltage-clamp techniques to isolated rabbit atrial myocytes. Whereas peak Ito1 exceeded Ito2 at slow rates (0.1 Hz), Ito1 was strongly reduced as rate was increased (by 97 +/- 2%, mean +/- SE, at 4 Hz), while Ito2 was slightly reduced (by 28 +/- 4%, 4 Hz). The reversal potential of transient outward tail currents at 0.07 Hz was -49 +/- 9 mV, while at 2.5 Hz the reversal potential became -18 +/- 7 mV (calculated Cl- reversal potential -18 mV). The addition of the Cl- transport blocker 4,4'-diisothiocyanostilbene-2,2'-disulfonic acid (DIDS; 150 microM) or the replacement of external Cl- with methanesulfonate inhibited a large part of the transient outward current elicited by depolarization at 4 Hz. DIDS and Cl- replacement increased action potential duration in both single rabbit atrial cells and multicellular rabbit atrial preparations. We conclude that the Ca(2+)-dependent Cl- current is substantially larger than the transient K+ current at physiological rates in the rabbit and is likely to play a more important role in action potential repolarization than the latter current in this tissue in vivo.

4-Aminopyridine↗
PubMed1995

Comparative mechanisms of 4-aminopyridine-resistant Ito in human and rabbit atrial myocytes.

The cardiac transient outward current (Ito) has been shown in several species to consist of two components: 1) a 4-aminopyridine (4-AP)-sensitive component (Ito1) and 2) a 4-AP-resistant component (Ito2). In rabbits, Ito2 is a Ca(2+)-dependent Cl- current [ICl(Ca)]; similar mechanisms have been suggested to underlie Ito2 in human atrium. We used whole cell patch-clamp techniques to define the mechanism of Ito2 (defined as the component resistant to 5 mM 4-AP) in human atrial myocytes, with parallel experiments performed in rabbit atrial cells. In rabbit atrium, Ito2 activated more slowly than Ito1 and had a bell-shaped current-voltage of Ito with properties similar to Ito2 in the rabbit, and a similar component recorded with pipette K+ replaced by Cs+ was suppressed by the substitution of methanesulfonate for Cl- in the superfusate. In human cells, a 4-AP-resistant Ito2 was recorded at a depolarizing pulse frequency of 1 Hz, but not at 0.1 Hz. Ito2 activated rapidly and inactivated earlier than Ito1, whereas its I-V relation was linear like that of Ito1. Ryanodine had no effect on human atrial Ito. When K(+)-free pipette solutions were used, no Ito was recorded in 30 human atrial myocytes, and external Cl- replacement with methanesulfonate failed to reveal an Ito. In 13 human myocytes, isoproterenol increased ICa but failed to activate an Ito compatible with ICl(Ca). Whereas caffeine suppressed human atrial Ito, it also suppressed Ito1 [in the presence of 200 microM Cd2+ to block ICa and 5 mM intracellular ethylene glycol-bis(beta-aminoethyl ether)-N,N,N',N'-tetraacetic acid to buffer intracellular Ca2+] in both human and rabbit atrium, indicating an action unrelated to Ca(2+)-triggered Ca2+ release. In conclusion, we were unable to demonstrate the presence of ICl(Ca) in human atrial myocytes, and the 4-AP-resistant component of Ito appeared to be due to 4-AP unblocking.

4-Aminopyridine↗
PubMed1995

Functional consequences of substitutions of the carboxyl residue glutamate 779 of the Na,K-ATPase.

Carboxyl-containing amino acids in the transmembrane segments appear to be important for sodium- and potassium-activated adenosinetriphosphatase (Na,K-ATPase) activity. Substitution of Glu779 with Leu in a ouabain-resistant isoform inactivates the overall enzyme activity (Jewell-Motz & Lingrel, 1993). Chemical modification of this residue results in inactivation of Na,K-ATPase in a Na+ and K+ protectable manner (Arguello and Kaplan, 1991, 1994). These experiments suggest that this residue is important in cation binding. To further understand the role of Glu779 in Na,K-ATPase function, we have substituted this with four amino acids (Gln, Asp, Ala, and Leu) using site-directed mutagenesis coupled with expression and characterized the expressed enzyme. The amino acid substitutions were introduced into a modified sheep RD alpha 1 isoform that is relatively resistant to this drug. Enzyme carrying the E779Q and E779A replacements conferred ouabain resistance to the sensitive HeLa cells, while expression of enzyme carrying the E779D and E779L substitutions did not. Further analysis of isolated plasma membranes containing altered enzymes E779Q and E779A confirmed that they retain Na,K-ATPase activity. Analysis of cation stimulation of Na,K-ATPase activity revealed that the E779Q substituted enzyme exhibited a similar apparent affinity for K+ and a 2.6-fold decrease in affinity for Na+ compared with control enzyme. The E779A replacement caused a 6.6-fold and 5-fold decrease in apparent affinity for K+ and Na+, respectively. There is no difference in apparent affinity for ATP at the low affinity site for either E779Q or E779A.(ABSTRACT TRUNCATED AT 250 WORDS)

Adenosine Triphosphate↗
PubMed1995

Effects of mebendazole, albendazole and praziquantel on alanine aminotransferase and aspartate aminotransferase of Echinococcus granulosus cyst wall harbored in mice.

Alanine aminotransferase (ALT) and aspartate aminotransferase (AST) of Echinococcus granulosus cyst wall harbored in mice for 10-12 months was measured. The activities of the 2 enzymes were 3,430 +/- 1,370-4,160 +/- 1,790 and 1,560 +/- 840-2,890 +/- 1,470, respectively. When infected mice were treated ig with mebendazole (Meb) 25 mg.kg-1.d-1 for 7-14 d, or 50 mg.kg-1.d-1 for 7 d, the ALT activities of cyst walls of both collapsed and full cysts were inhibited significantly with average inhibition rates of about 50%. Another benzimidazole derivative, albendazole (Alb), also inhibited ALT activity of the cyst wall with an inhibition rate of 40.7%, but this was not the case in the treatment with praziquantel 500 mg.kg-1.d-1 of the infected mice for 14 d. When the infected mice were treated ig with the above mentioned drugs at the same regimens, no apparent effect on AST activities of the cyst wall was seen except for the group treated ig with Meb at a higher daily dose, the inhibition rates being 26% (collapsed cyst) and 43.9% (full cyst). The significance of the results has been discussed briefly.

Alanine Transaminase↗
PubMed1995

Detection of a 67-kD glycoprotein in human tumor cell lines by a monoclonal antibody established against a recombinant human endogenous retrovirus-K envelope-gene-encoded protein.

Endogenous retroviruses in humans are discussed as putative etiologic agents in tumorigenesis. Molecular mimicry of cellular epitopes by retroviruses may be of importance for the genesis of autoimmune diseases. A group of human endogenous retroviruses, HERV-K, which is related to the mouse mammary tumour virus, has been characterised previously and open reading frames have been found covering their gag, pol, prt and env genes. Transcription of HERV-K genomes at the mRNA level as well as antibodies in human sera directed against HERV-K env have been detected recently. We have generated a monoclonal antibody (mAb), anti-HERV1, against a recombinant HERV-K Env protein. This mAb is capable of immunoprecipitating a 67-kD glycoprotein from the human breast carcinoma cell line T47D, the amount of which is strongly enhanced after stimulation with estradiol followed by progesterone. The same band could be precipitated from other carcinoma cell lines (Hep2, MCF7 and HeLa), but not from the human B-lymphoblastoid cell line Raji and from cultured human fibroblasts. Incubation of this antigen in the presence of endoglycosidase F indicates the presence of N-linked carbohydrate moieties of at least 7-9 kD.

Animals↗
PubMed1995

[Observation of immune effect of 5 kinds of Denmark II lyophilized vaccines].

This paper reported five kinds of Denmark II lyophilized vaccines produced by 5 different biological production institutes. Through the double blind randomized trial in newborns after 1 year observation, the results demonstrated that all vaccines possessed the stability of heat tolerance and the 12 week tuberculin conversion rates of all group exceeded to 95%, and 1-year positive maintenance rates were in the range of 88.3%-96.1%, and the average diameter of induration was relatively large; the local reaction belonged to normal range; the swollen-lymph node rate was not high; the immune effect was satisfactory.

BCG Vaccine↗
PubMed1995

The relationship between secondary chromosomal abnormalities and blast transformation in chronic myelogenous leukemia.

Chronic myelogenous leukemia (CML) is a stem cell disorder which progresses from a chronic phase (CP) to an accelerated phase (AP), and/or a blast phase (BP) of myeloid (M) or lymphoid (L) phenotype. This progression is frequently preceded or accompanied by recurring secondary chromosomal abnormalities which are believed to play a role in the transformation. In order to investigate the relationship between the secondary change and the development of BP, we undertook a study using fluorescence in situ hybridization to determine in which cells the secondary abnormalities were present. We observed that in one case of L-BP, the secondary change (trisomy 8) appeared to be in a subclone that was different from the blast cells, as it was absent from the lymphoblasts but present in differentiating erythroid, monocytic and granulocytic cells. In two cases, the secondary change (trisomy 8, extra Ph) probably occurred prior to an acute transforming event as it was present in CP or AP predominantly in differentiated granulocytic or monocytic cells. In one case of M-BP, the secondary change (trisomy 8) probably occurred after the acute transformation, as it appeared in only a subset of the blasts. Lastly, in four cases of L-BP, the secondary change (monosomy 7, extra Ph or hyperdiploidy) was closely associated with the BP as it was present in all of the blasts. The findings indicate that some secondary abnormalities may be directly related to the development of BP and may provide clues to the identity of genes responsible for the acute phase transition. Other abnormalities occurring before, or after the acute transformation or in a different subclone from the acute phase blasts, may be more important for denoting genomic instability than for helping to understand the mechanism of blast transformation.

Adolescent↗
PubMed1995

Effect of antihydatid drugs on carbohydrate metabolism of metacestode of echinococcus granulosus.

A biochemical some enzymes of glycolysis and a partial reversed tricarboxylic acid cycle together with hydrolytic enzymes in the cyst wall of Echinococcus granulosus was carried out. Lactate dehydrogenase (LDH), pyruvate kinase (PK), phosphoenolpyruvate carboxykinase (PEPCK), and adenosine triphosphatase (ATPase) showed their high level of activity, suggesting that the proliferation of E. granulosus cyst wall is an energy-dependent process and the major pathways for glucose metabolism is glycolysis. Treatment of E. granulosus-infected mice with mebendazole and albendazole resulted in marked inhibition of PK, PEPCK and ATPase of E. granulosus cyst wall, whereas praziquantel had no effect, indicating that PK, PEPCK, and ATPase might be chemotherapeutic targets and the differences in the inhibitory effects might account for the efficacy of the three antihydatid drugs.

Adenosine Triphosphatases↗
PubMed1995

[Preoperative embolization of paraganglioma in head and neck].

Preoperative embolization of 10 cases of paraganglioma in carotid artery body and jugular foramen region via endovascular approach was performed. Tumor vessels were obliterated 100% in 7 cases and 80% - 90% in 3 cases as was demonstrated by angiography. It is available for us to reduce bleeding, expose tumor, avoid the iatrogenic damage of the important vessels and nerves around tumor during operation and to total resection possible. Additionally, the manipulating points of embolization are discussed.

Adult↗
PubMed1995

[Cloning and analysis of prophage PBSX repressor gene from Bacillus subtilis].

The repressor gene and its allele--a temperature sensitive mutant have been cloned from the defective prophage PBSX of Bacillus subtilis by means of PCR technique. The characterization of these sequences suggest that wild-type and mutant gene have the same open reading frame, which probably encode a repressor protein of 113 amino acids, and the putative promoter region and ribosome binding sites within the sequences have also been identified. The results from complementation experiments demonstrate that repressor encoded by wild-type gene is capable of blocking the temperature-shift to induce PBSX prophage in Bacillus subtilis.

Amino Acid Sequence↗
PubMed1994

Two mutant alleles of mukB, a gene essential for chromosome partition in Escherichia coli.

The MukB protein is essential for chromosome partitioning in Escherichia coli and consists of 1484 amino acid residues (170 kDa). We have determined the base changes at the mutated sites of the mukB106 mutant and a newly isolated mutant, mukB33. These mutant mukB genes were each found to carry a single base-pair transition which leads to an amino acid substitution; a serine residue at position 33 was changed to phenylalanine in the case of mukB106, and an aspartic acid residue at position 1201 was changed to asparagine in the case of mukB33.

Alleles↗