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Biomedical subjects

R Zhang

Publications and source records attributed to R Zhang.

At least 415 records · Page 23Linked to original sources
PubMed1995

Endothelin analogs which distinguish vasoconstrictor and vasodilator ETB receptors.

[Pen 1,11, Nle7, Glu9, Ala18]-Sarafotoxin S6b (BMS-184696) and [Pen1,11, Nle7, Glu9, Leu18]-sarafotoxin S6b (BMS-184697) were synthesized with the aim of preparing ETB receptor antagonists. BMS-184696 was a potent ETA antagonist, an extremely potent vasoconstrictor ETB agonist, and a non-competitive vasodilator ETB antagonist with no agonist activity. BMS-184697 was a potent ETA antagonist, a potent vasoconstrictor ETB agonist, and a vasodilator ETB agonist with moderate potency. The ability of BMS-184696 to activate the vasoconstrictor ETB receptor but not the vasodilator ETB receptor, despite having high affinity binding to the vasodilator ETB receptor as evidenced by its antagonist activity, strongly suggests the existence of ETB receptor subtypes.

Animals↗
PubMed1995

Synthesis, conformation and opioid activity of deltorphins.

A series of deltorphin analogues was prepared by solid-phase peptide synthesis. Their opioid activity was evaluated in rat opiatic assay and their conformation was determined by two-dimension Nuclear Magnetic Resonance Spectroscopy. The analogues containing D-alanine acid at position 2 were much more potent in the assay than their corresponding isomers containing L-alanine acid at this position. The conformational analysis on NMR study in DMSO showed that C-terminal tetrapeptides of both deltorphin II and its L-alanine analog might form a 3(10) helix, which confirms that the substitution of D-amino acid at position 2 decreased the opioid activity.

Analgesics↗
PubMed1995

Calcium entry blockers and activators: conformational and structural determinants of dihydropyrimidine calcium channel modulators.

Dihydropyrimidines 4, 6, and 15, uniquely designed to unambiguously establish structural and conformational determinants for DHP receptor occupation and for modulation of calcium channel function, were prepared and examined for calcium channel modulation. Our results confirm and firmly establish a preference for syn-orientation of an unsymmetrically substituted aryl moiety at the DHP receptor (15d vs 15e). We propose a normal vs capsized DHP boat model to explain structural and conformational requirements for modulation of calcium channel function that requires an obligatory left-hand side alkoxy cis-carbonyl interaction for maximal DHP receptor affinity, the effect of channel function being determined by orientation of the 4-aryl group. Enantiomers having an up-oriented pseudoaxial aryl group (normal DHP boat) will elicit calcium antagonist activity, whereas enantiomers having a down-oriented pseudoaxial aryl group (capsized DHP boat) will elicit calcium agonist activity. Single enantiomers of macrocyclic lactone 15b demonstrate opposite channel activity. Antagonist activity resides in enantiomer 15b-A (S-configuration, left-hand side alkoxy cis-carbonyl with up-oriented pseudoaxial aryl group and normal DHP boat), whereas agonist activity resides in enantiomer 15b-B (R-configuration, left-hand side alkoxy cis-carbonyl with down-oriented pseudoaxial aryl group and capsized DHP boat). Moreover, this model is consistent with and provides a rational explanation of previous literature in this area, most notably the observation of chiral inversion and potency diminution upon replacement of ester by hydrogen in the Bay K 8644 series.

Animals↗
PubMed1995

Glycine 122 is essential for cooperativity and binding of Mg2+ to porcine fructose-1,6-bisphosphatase.

Site-directed mutagenesis of an amino acid residue in the substrate binding site of porcine fructose-1,6-bisphosphatase was carried out based on the crystal structure of the enzyme (Zhang, Y., Liang, J.-Y., Huang, S., Ke, H., and Lipscomb, W. N. (1993) Biochemistry 32, 1844-1857). A mutant enzyme form of fructose-1,6-bisphosphatase, G122A, was purified and characterized by sodium dodecyl sulfate-polyacrylamide gel electrophoresis, circular dichroism spectrometry (CD), and initial rate kinetics. There were no discernible differences between the secondary structures of the wild-type and the mutant enzyme on the basis of CD data. Altering Gly-122 to alanine caused a significant decrease in the enzyme's activity and affinity for Mg2+. The kcat for this mutant enzyme was only about 5% of that of wild-type fructose-1,6-bisphosphatase, and the Ka for Mg2+ was about 20-fold higher than that of the wild-type enzyme. The Ki for AMP was increased 77-fold in the case of the mutant enzyme; however, the Hill coefficient was unaltered. Most importantly, it was observed that replacement of Gly-122 with alanine caused the total loss of cooperativity for Mg2+. It is concluded that Gly-122 is essential for Mg2+ cooperativity and important for binding of Mg2+ and AMP as well as for enzyme activity.

Animals↗
PubMed1995

Transcriptional induction of the melanocyte-stimulating hormone receptor in brain metastases of murine K-1735 melanoma.

Metastatic K-1735 murine melanoma cells are amelanotic in culture or in the subcutis of syngeneic mice. When injected into the internal carotid artery, these cells produce melanotic brain metastases. The production of melanin in tumor cells growing in the brain was directly correlated with induction of melanocyte-stimulating hormone receptor (MSH-R) steady-state mRNA transcripts. K-1735 cells isolated from brain lesions and implanted into the subcutis or grown in culture lose MSH-R transcripts and become amelanotic. In contrast to K-1735 cells, B16-BL6 melanoma cells constitutively produce melanin and express high levels of MSH-R mRNA regardless of the site of growth. Somatic cell hybrids between K-1735 and B16 cells produced melanin and expressed high levels of MSH-R mRNA transcripts, regardless of the site of growth, suggesting the dominance of the B16 phenotype. Treatment with alpha-MSH failed to upregulate MSH-R expression in cultured K-1735 cells or to maintain MSH-R expression in K-1735 cells isolated from brain metastases to be grown in culture. Responsiveness to alpha-MSH as determined by cell proliferation, melanin production, and intracellular accumulation of cyclic AMP directly correlated with MSH-R expression. These data demonstrate that a specific organ environment influences the phenotype of metastatic cells by regulation of specific genes that encode for cell surface receptors.

Animals↗
PubMed1995

Liposome capillary electrophoresis for analysis of interactions between lipid bilayers and solutes.

Liposomes, which mimic biomembranes, were used as a pseudostationary phase in capillary zone electrophoresis. The decrease in the mobility of an analyte owing to the presence of liposomes reflected interaction between the analyte and the liposomes. Equations were derived to calculate the specific capacity factor Ks (the capacity factor, k', normalized to the liposome concentration 1 M) from the migration times and to estimate the difference in free energy, delta(delta G0), of the weak analyte/liposome interactions. The order of Ks values for the drugs tested was aspirin < salicylic acid < warfarin << sulfasalazine. The peptide TyrGlySerThrProGlyCysCys interacted more strongly with the liposomes (Ks = 10.1 M-1) than did TyrGlySerThrProGlySerSer (Ks = 9.1 M-1). These results were similar to those obtained earlier by immobilized liposome chromatography.

Amino Acid Sequence↗
PubMed1995

Rat tail suspension reduces messenger RNA level for growth factors and osteopontin and decreases the osteoblastic differentiation of bone marrow stromal cells.

We previously reported that bone marrow stromal cells produce insulin-like growth factors (IGF-I and -II), and that medium conditioned by marrow stromal cells stimulates osteoblast proliferation in vitro. The present study employed the rat tail-suspension model to unload the hindlimbs. It was designed to test the hypothesis that the development of osteopenia or osteoporosis could be due to a deficit in the osteogenic function of marrow stromal cells. Although tail suspension suppressed body weight during the first 3 days of an 11-day pair-fed study, the overall weight gain recorded by these animals was normal. Nevertheless, bone growth was inhibited by suspension. Similarly, the total adherent marrow stromal cell population harvested from the femurs and tibias was decreased by tail suspension, and only half the normal number of fibroblastic stromal cell colonies grew when they were cultured. The proliferation of alkaline-phosphatase-positive cells in the stroma was also inhibited. Northern hybridization revealed that the messenger RNA level for transforming growth factor-beta 2 and IGF-II in stromal cell was reduced by tail suspension. The production of IGF-II by marrow stromal cells was also decreased. The steady-state level of five different transcript sizes of IGF-I mRNA was altered differentially by tail suspension. Osteopontin mRNA was also reduced in marrow stromal cells from tail-suspended rats compared with the normal rats. These data suggest that skeletal unloading not only alters the mRNA level for growth factors and peptide production, but also affects the proliferation and osteogenic differentiation of marrow stromal cells. These changes may be responsible for the reduced bone formation in osteopenia and osteoporosis.

Animals↗
PubMed1995

Properties and regulation of 17 beta-hydroxysteroid oxidoreductase of OVCAR-3, CAOV-3, and A431 cells: effects of epidermal growth factor, estradiol, and progesterone.

Although there is a growing body of evidence that 17 beta-hydroxysteroid oxidoreductase plays a role in the regulation of steroid levels in epithelial tumors of the endometrium and breast, our knowledge of its role in other gynecologic tumors is limited. In this investigation, the 17 beta-hydroxysteroid oxidoreductase activity of cell lines derived from two ovarian tumors (OVCAR-3, CAOV-3) and an epidermoid tumor of the vulva (A431) was assayed under conditions which differentiate between 17 beta-hydroxysteroid oxidoreductase type 1, a cytosolic isoform highly specific for estradiol, and type 2, a membrane bound isoform reactive with both estradiol and testosterone. On the basis of estradiol/testosterone activity ratios, all three cell lines appear to have type 2-like activity, with the specific activity of A431 markedly greater than that of the other cell lines. Estradiol, progesterone, or EGF, alone or in combination, were without effect on the enzymatic activity of OVCAR-3 cells. EGF decreased the activity of CAOV-3 cells slightly. In contrast, EGF stimulated A431 17 beta-hydroxysteroid oxidoreductase activity 7-8-fold over a 5-day exposure. Estradiol or progesterone, singly or in combination, also did not effect the enzymatic activity of A431 cells. However, progesterone inhibited the increase in activity seen in the presence of EGF. With EGF, estradiol, and progesterone together, the increase in enzymatic activity was comparable to that with EGF alone. The effects of estradiol and progesterone appear to result from steroid actions following binding of EGF to low-affinity receptors on A431 cells.

Epidermal Growth Factor↗
PubMed1995

Proton nuclear magnetic resonance studies on huwentoxin-I from the venom of the spider Selenocosmia huwena: 1. Sequence-specific 1H-NMR assignments.

The complete sequence-specific assignments of resonances in the 1H-NMR spectrum of huwentoxin-I from the Chinese bird spider, Selencocosmia huwena, is described. A combination of two-dimensional NMR experiments including 2D-COSY, 2D-NOESY, and 2D-TOCSY has been employed on samples of the toxin dissolved in D2O and in H2O for assignment purposes. Protons belonging to spin systems for each of the 33 amino acids were identified. The sequence-specific assignments were facilitated by the identification of d alpha N connectivities on the fingerprint regions of the COSY and NOESY spectra and were supported by the identification of dNN and d alpha N connectivities in the TOCSY and NOESY spectra. These studies provide a basis for the determination of the solution-phase conformation of this toxin.

Amino Acid Sequence↗
PubMed1995

Pharmacokinetics of an anti-human immunodeficiency virus antisense oligodeoxynucleotide phosphorothioate (GEM 91) in HIV-infected subjects.

Human pharmacokinetics of an antisense oligodeoxynucleotide phosphorothioate (GEM 91) developed as an anti-human immunodeficiency virus (HIV) agent was carried out in this study. 35S-Labeled GEM 91 was administered to six HIV-infected individuals by means of 2-hour intravenous infusions at a dose of 0.1 mg/kg. Plasma disappearance curves for GEM 91-derived radioactivity could be described by the sum of two exponentials, with half-life values of 0.18 +/- 0.04 and 26.71 +/- 1.67 hours. The radioactivity in plasma was further evaluated by polyacrylamide gel electrophoresis, showing the presence of both intact GEM 91 and lower molecular weight metabolites. Urinary excretion represented the major pathway of elimination, with 49.15% +/- 6.80% of the administered dose excreted within 24 hours and 70.37% +/- 6.72% over 96 hours after dosing. The radioactivity in urine was associated with lower molecular weight metabolites. No drug-related toxicity was observed.

Adult↗
PubMed1995

Population characteristics of hepatic dihydropyrimidine dehydrogenase activity, a key metabolic enzyme in 5-fluorouracil chemotherapy.

Dihydropyrimidine dehydrogenase is the initial rate-limiting enzyme in catabolism of 5-fluorouracil, one of the most widely used cancer chemotherapeutic agents. Previous studies have shown the clinical importance of determination of dihydropyrimidine dehydrogenase in patients with cancer, particularly in those with deficiency of this enzyme who experience severe 5-fluorouracil-associated toxicity (including death) after 5-fluorouracil treatment. In the present study, dihydropyrimidine dehydrogenase activity was determined in 138 donor liver samples. A normal distribution of human liver dihydropyrimidine dehydrogenase activity was shown. The mean enzyme activity was compared across different groups by age, gender, and race, with no significant differences observed except that the mean enzyme activity in women was slightly higher than that observed in men. With use of a polyclonal antibody generated against human liver dihydropyrimidine dehydrogenase, Western blot analysis showed that dihydropyrimidine dehydrogenase protein in the liver cytosol correlated with the activity of this enzyme.

Adult↗
PubMed1995

Comparison of the free and DNA-complexed forms of the DNA-binding domain from c-Myb.

The DNA-binding domain of c-Myb consists of three imperfect tandem repeats (R1, R2 and R3). The three repeats have similar overall architectures, each containing a helix-turn-helix variation motif. The three conserved tryptophans in each repeat participate in forming a hydrophobic core. Comparison of the three repeat structures indicated that cavities are found in the hydrophobic core of R2, which is thermally unstable. On complexation with DNA, the orientations of R2 and R3 are fixed by tight binding and their conformations are slightly changed. No significant changes occur in the chemical shifts of R1 consistent with its loose interaction with DNA.

Amino Acid Sequence↗
PubMed1995

Structures of cDNAs encoding the muscle-type and non-muscle-type isozymes of lamprey fructose bisphosphate aldolases and the evolution of aldolase genes.

Nearly full-length cDNA clones for muscle-type and non-muscle-type aldolase mRNAs were cloned from lambda gt10 cDNA libraries constructed from skeletal muscle and liver mRNAs of lamprey (Entosphenus japonicus). The cDNA-M8 has 2,240 bp carrying an open reading frame of 1,089 bp which encodes 362 amino acids without the amino terminal methionine, while the cDNA-L3 is 1,761 bp in length and has an open reading frame of 1,092 bp, which encodes 363 amino acids without the methionine. We designated the cDNA clones M8 and L3 as the muscle-type and non-muscle-type aldolase cDNAs, respectively. The entire amino acid sequences deduced from cDNA-M8 and -L3 show a high degree of identity to one another (76%) and also to vertebrate aldolases A (74-76%), B (68-70%), and C (71-76%) and Drosophila melanogaster aldolases alpha, beta, and gamma (66-67%). Northern blot analyses using the 3'-noncoding sequences of cDNA-M8 and -L3 as hybridization probes indicated that the muscle-type mRNA is expressed mainly in the skeletal muscle, heart muscle, brain, and some other tissues, but probably not in liver, while the non-muscle-type mRNA is expressed mainly in the liver and also in brain and other tissues, except for the heart muscle. Phylogenetic analyses showed that both muscle-type and non-muscle-type aldolases of lamprey resemble one another and might share a common ancestor with vertebrate aldolases A and C, but they are not direct ancestors of vertebrate aldolases.

Amino Acid Sequence↗
PubMed1995

Drosophila melanogaster aldolase: characterization of the isozymes alpha, beta, and gamma generated from a single gene.

Three isozymic forms, alpha, beta, and gamma, of Drosophila melanogaster aldolase are produced from a single gene by alternative usage of the triple exons 4 (4 alpha, 4 beta, and 4 gamma) [Shaw-Lee et al. (1992) J. Biol. Chem. 267, 3959-3967; Kim et al. (1992) Mol. Cell. Biol. 12, 773-783; Kai et al. (1992) J. Biochem. 112,677-688]. The expression plasmids for the respective isozymes were transfected into Escherichia coli cells, and the isozymes alpha and beta were purified to homogeneity by a simple procedure, though isozyme gamma was only partially purified. These isozymes are active towards two substrates, fructose-1,6-bisphosphate (Fru-1,6-P2) and fructose-1-phosphate (Fru-1-P), with a preference for Fru-1,6-P2 over Fru-1-P, but they have different kcat/Km values towards these two substrates; isozyme alpha shows the highest value for Fru-1,6-P2. These isozymes show similarity in optimal pHs, thermal stability, and Km values for both Fru-1,6-P2 and Fru-1-P. They are composed of four identical subunits of 40 kDa, forming a tetramer with a molecular weight of approximately 160 kDa. The three isozymes are different in primary structure only at the carboxyl-terminal region encoded by the respective exon 4. Therefore, this region should be primarily responsible for the distinct characteristics of these isozymes.

Amino Acid Sequence↗
PubMed1995

Cardiac troponin I phosphorylation increases the rate of cardiac muscle relaxation.

Cardiac troponin (Tn) I (CTnI), compared with skeletal TnI, contains extra amino acids (32 to 33) at its amino terminus, including two adjacent serine residues. These two serine residues are believed to be phosphorylated by protein kinase A (PKA) upon stimulation of the heart by beta-agonists. In this study, we found that phosphorylation of a cardiac skinned muscle preparation by PKA, mainly at CTnI, results in a decrease in the Ca2+ sensitivity of muscle contraction. The pCa50 decreased by approximately 0.27 +/- 0.06 pCa units upon phosphorylation. To study cardiac muscle relaxation, we used diazo-2, a photolabile Ca2+ chelator with a low Ca2+ affinity in its intact form that is converted to a high-affinity form after photolysis. We found that the rate of cardiac muscle relaxation increased from a time of half-relaxation (t1/2) = 110 +/- 10 milliseconds to t1/2 = 70 +/- 8 milliseconds after CTnI phosphorylation. This result demonstrates that CTnI phosphorylation can be linked with the increased rate of muscle relaxation in a relatively intact muscle preparation. Since CTnI phosphorylation has been shown previously to affect the Ca2+ affinity and Ca2+ off-rate of CTnC in vitro, it is likely that the faster relaxation seen here reflects faster dissociation of Ca2+ from cardiac TnC (CTnC). Model calculations show that increased dissociation of Ca2+ from CTnC, coupled with the faster uptake of Ca2+ by the sarcoplasmic reticulum stimulated by PKA phosphorylation of phospholamban, can account for the faster relaxation seen in the inotropic response of the heart to catecholamines.

Adenosine Triphosphatases↗
PubMed1995

[My personal idea on authorship of Nanjing (Classic of Questioning)].

It has been a matter of dispute on the authorship, date of writing of Nanjing (Classic of Questioning). This paper mentions 2 evidences based on the Classic's academic idea and its developmental history and 3 collateral evidences from literatures of the Han Dynasty, claiming that Nanjing was written in the period of Warrings States by Qin Yueren. This is of significance in the assessment of the position and influence of Nanjing in the history of TCM.

China↗
PubMed1995

[The effective time of HX solution for rat liver preservation].

The effects of HX solution and UW solution for rat liver preservation were studied with non-circulated isolated perfused rat liver model. Sixty-six inbred Wistar rat livers were randomly preserved for 12, 18, 24, and 30h with HX solution or UW solution. The effects were assessed by measuring hepatic tissue water content, sinusoidal lining cell mortality, Krebs-Henseleit's perfusate aspartate aminotransferase, the number of livers secreting bile during isolated perfusion, and by observing the morphological changes in liver. The experimental results suggest that the effects of HX solution for rat liver preservation be similar to those of UW solution within 24h storage.

Adenosine↗