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Biomedical subjects

Z R Liu

Publications and source records attributed to Z R Liu.

At least 19 recordsLinked to original sources
PubMed2006

Facile synthesis of optically pure (S)-3-p-hydroxyphenyllactic acid derivatives.

Optically pure (S)-3-p-hydroxyphenyllactic acid derivatives are important intermediates of peroxisome proliferator-activated receptor alpha/gamma dual agonists and heteropeptides. Many efforts have been made for synthesis of those intermediates, but there exist some flaws yet. We observed that dielectric constants of organic solvents drastically affected diazotization of O-benzyl-L-tyrosine. Optically pure (S)-3-p-benzyloxyphenyllactic acid was obtained by simple recrystallization when DMF or DMSO of higher dielectric constant was used as a co-solvent in diazotization of O-benzyl-L-tyrosine. It was easily turned into various optically pure (S)-3-p-hydroxyphenyllactic acid derivatives.

Molecular Conformation↗
PubMed2001

Metal binding affinity and structural properties of an isolated EF-loop in a scaffold protein.

To establish an approach to obtain the site-specific calcium binding affinity of EF-hand proteins, we have successfully designed a series of model proteins, each containing the EF-hand calcium-binding loop 3 of calmodulin, but with increasing numbers of Gly residues linking the loop to domain 1 of CD2. Structural analyses, using different spectroscopic methods, have shown that the host protein is able to retain its native structure after insertion of the 12-residue calcium-binding loop and retains a native thermal stability and thermal unfolding behavior. In addition, calcium binding to the engineered CD2 variants does not result in a significant change from native CD2 conformation. The CD2 variant with two Gly linkers has been shown to have the strongest metal binding affinity to Ca(II) and La(III). These experimental results are consistent with our molecular modeling studies, which suggest that this protein with the engineered EF-loop has a calmodulin-like calcium binding geometry and backbone conformation. The addition of two Gly linkers increases the flexibility of the inserted EF-loop 3 from calmodulin, which is essential for the proper binding of metal ions.

Amino Acid Motifs↗
PubMed2001

[Determination of rate constants of gas-phase reactions of alpha-pinene and beta-pinene with ozone].

alpha-pinene and beta-pinene are the most dominating species among natural terpenes. Terpenes are mainly emitted from forest trees, flowers and grass. In the lower troposphere terpenes can react fast with OH radical, ozone, NO3 radical and ground state oxygen atom. These reactions may contribute to the occurring of aerosols, peroxides (hydrogen peroxide and organic peroxide), carbon cycle (mainly CO), acid rain (organic acids, NO3- and SO4(2-), ozone and active radicals such as OH radical. Reactions with ozone occur both in the daytime and in the night. The study in this field in China began in the late 1980. The main work focus on the source emission and the experimental simulation has just started. It is most of our group's work. In this paper preliminary experimental simulation of the gas-phase reactions of alpha-pinene and beta-pinene with ozone were carried out in the quartz chamber. The rate constants of these reactions were measured using long-path Fourier transform infra-red combined with relative rate constant method. And the rate constants for the gas-phase reactions of alpha-pinene, beta-pinene with ozone were determined as 2.83 x 10(17) cm3.molecule-1.s-1 and 1.48 x 10(17) cm3.molecule-1.s-1 at 1.0 x 10(5) Pa and 296 +/- 3 K. The results are quite similar to the data from Atkinson group. No cyclohexane was added to the reaction system during the measurement to restrain the formation of OH radical. The formation of OH radical could not be quantified, so that the effect of subsidiary reactions induced by OH radical has not been calculated. In the later simulation study and model this effect should be considered.

Acid Rain↗
PubMed2000

Identification of a locus for disseminated superficial actinic porokeratosis at chromosome 12q23.2-24.1.

Disseminated superficial actinic porokeratosis is an autosomal dominant cutaneous disorder characterized by many uniformly small, minimal, annular, anhidrotic, and keratotic lesions. The genetic basis for this disease is unknown. Using a genomewide search in a large Chinese family, we identified a locus at chromosome 12q23.2-24. 1 responsible for disseminated superficial actinic porokeratosis. The fine mapping study indicates that the disseminated superficial actinic porokeratosis gene is located within a 9.6 cM region between markers D12S1727 and D12S1605, with a maximum two-point LOD score of 20.53 (theta = 0.00) at D12S78. This is the first locus identified for a genetic disease where the major phenotype is porokeratosis. The study provides a map location for isolation of a gene causing disseminated superficial actinic porokeratosis.

China↗
PubMed1998

Detection of a novel ATP-dependent cross-linked protein at the 5' splice site-U1 small nuclear RNA duplex by methylene blue-mediated photo-cross-linking.

Assembly of spliceosomes involves a number of sequential steps in which small nuclear ribonucleoprotein particles (snRNPs) and some non-snRNP proteins recognize the splice site sequences and undergo various conformational rearrangements. A number of important intermolecular RNA-RNA duplexes are formed transiently during the process of splice site recognition. Various steps in the assembly pathway are dependent upon ATP hydrolysis, either for protein phosphorylation or for the activity of helicases, which may modulate the RNA structures. Major efforts have been made to identify proteins that interact with specific regions of the pre-mRNA during the stages of spliceosome assembly and catalysis by site-specific UV cross-linking. However, UV cross-linking is often inefficient for the detection of proteins that interact with base-paired RNA. Here we have used the complementary approach of methylene blue-mediated photo-cross-linking to detect specifically proteins that interact with the duplexes formed between pre-mRNA and small nuclear RNA (snRNA). We have detected a novel cross-link between a 65-kDa protein (p65) and the 5' splice site. A range of data suggest that p65 cross-links to the transient duplex formed by U1 snRNA and the 5' splice site. Moreover, although p65 cross-linking requires only a 5' splice site within the pre-mRNA, it also requires ATP hydrolysis, suggesting that its detection reflects a very early ATP-dependent event during splicing.

Adenosine Triphosphate↗
PubMed1997

Crosslinking of the U5 snRNP-specific 116-kDa protein to RNA hairpins that block step 2 of splicing.

Step 2 of pre-mRNA splicing has characteristics that are suggestive of a 5' to 3' scanning process from the branch point to locate the 3' splice site. Specifically, the 3' splice site is almost always at the first AG downstream of the branch point even when the two elements are separated by hundreds of nucleotides. Insertion of new AGs between the branch and 3' splice site, or mutation of the wild-type 3' splice site, usually results in use of the new first AG as the 3' splice site. Finally, insertion of stable secondary structure between the branch point and 3' splice site, but distant from both elements, results in a block to step 2. We have sought to complement this circumstantial evidence by detecting physical contacts between the spliceosome and the RNA substrate in regions that are not themselves important for splicing, other than that they lie between the branch point/polypyrimidine tract and the 3' splice site. We have blocked step 2 of splicing by insertion of hairpin structures between the branch point and 3' splice site and applied methylene blue-mediated crosslinking, which is specific for protein-dsRNA interactions. Using this approach, we have detected a 116-kDa crosslinked protein that appears after step 1 of splicing with all transcripts containing a hairpin downstream of the branch point. The protein was identified as the 116-kDa U5 snRNP protein, which is a GTP-binding protein involved in step 2 of splicing. The crosslinking characteristics of U5 p116 are consistent with it having a role in locating the 3' splice site AG prior to step 2 of splicing.

HeLa Cells↗
PubMed1996

N,N'-bis[3,3'-(dimethylamino)propylamine]-3,4,9, 10-perylenetetracarboxylic diimide, a dicationic perylene dye for rapid precipitation and quantitation of trace amounts of DNA.

A novel dicationic dye with a polycyclic aromatic perylene core and flexible cationic side chains- N,N'-bis[3, 3'-(dimethylamino)propylamine]-3,4,9,10-perylenetetracarboxylic diimide-termed "DAPER," was synthesized and characterized. The dye appears to exist in a highly stacked form in aqueous solution. DAPER precipitates extremely low concentrations of DNA very rapidly, efficiently, and with a stoichiometry of one tightly bound dye per DNA base pair, corresponding to a neutral complex. Precipitation may occur due to side-by-side association between the polyanionic DNA helix and polycationic dye stacks. DNA precipitation by DAPER is less sensitive to DNA concentration and length, and prevailing salt concentrations, than precipitation with ethanol or propanol. DAPER can be quantitatively extracted from DNA into a standard phenol:chloroform mixture under slightly alkaline conditions. The recovered DNA is suitable for treatment with enzymes typically used in DNA sequencing procedures. The amount of DNA precipitated is accurately determined by visible absorption or fluorescence spectroscopic analyses of the phenol:chloroform extracts. Several samples of DNA can be precipitated, recovered, and quantitated in about 1 h using standard microscale procedures and equipment. The unique qualities of DAPER provide the basis for a very sensitive, rapid, and versatile method for simultaneous precipitation and quantitation of microgram and submicrogram amounts of DNA.

1-Propanol↗
PubMed1996

Selective DNA binding of (N-alkylamine)-substituted naphthalene imides and diimides to G+C-rich DNA.

Alkylamine-substituted naphthalene imides and diimides bind DNA by intercalation and have applications as anticancer agents. The unique structures of these imides in which two adjacent carbonyl groups lie coplanar to an extended aromatic ring system allow the possibility of sequence-selective interactions between the intercalated chromophore and guanine amino groups situated in the DNA minor groove. The binding affinities of N-[3-(dimethylamino)propyl amine]-1,8-naphthalenedicarboxylic imide (N-DMPrNI) and N,N'-bis [3,3'-(dimethylamino)propylamine]-naphthalene-1,4,5,8-tetracarboxylic diimide (N-BDMPrNDI) for natural DNAs of differing base composition were determined spectroscopically and by equilibrium dialysis. In agreement with the above proposition, binding studies indicated that both the naphthalene imide and diimide strongly prefer to intercalate into steps containing at least one G:C base pair. The dependencies of association constants on DNA base composition are consistent with a requirement for one G:C pair in the binding site of the monomide, and two G:C pairs in binding sites of the diimide. These selectivities are comparable to or exceed that of actinomycin D, a classic G:C-selective drug. Protection footprinting with DNase I confirmed that the naphthalene monoiimide (N-DMPrNI) prefers to bind adjacent to G:C base pairs, with a most consistent preference for "mixed" steps containing both a G:C and an A:T pair, excepting GA:TC. Several 5'-CG-3' steps were also good binding sites as indicated by nuclease protection, but few GC:GC or GG:CC steps were protected. The naphthalene diimide inhibited DNase I digestion, but did not yield a footprint. The base recognition ability and versatile chemistry make naphthalene imides and diimides attractive building blocks for design of highly sequence-specific, DNA-directed drug candidates including conjugated oligonucleotides or oligopeptides.

Amines↗
PubMed1996

Detection of double-stranded RNA-protein interactions by methylene blue-mediated photo-crosslinking.

Double-stranded(ds) RNA-binding proteins have diverse functions in the cell. An obstacle to investigating the interactions between these proteins and dsRNA is the relative inefficiency of traditional UV-crosslinking methods for extended regions of dsRNA. We have therefore developed an alternative procedure for RNA-protein photo-crosslinking that efficiently induces RNA-protein crosslinks in double-stranded regions of RNA. We show that dsRNA-protein crosslinks can be induced by visible light in the presence of the dye methylene blue, which most likely mediates crosslinking by intercalating in the dsRNA helix. A recombinant dsRNA binding domain from the Drosophila staufen protein and human protein kinase R were crosslinked by UV or methylene blue to a series of dsRNAs. In each case, the degree of crosslinking was greater with methylene blue, particularly with RNAs with few single-stranded loops. Methylene blue-mediated crosslinking therefore complements and extends the existing repertoire of crosslinking methods for detecting RNA-protein interactions.

Animals↗
PubMed1994

Experimental study of chuanxiong on cerebrovascular hemodynamic parameters.

In the experimental rabbit arteriosclerosis, the change of the cerebrovascular hemodynamic parameters (CVHP) and the effect of Chuanxiong (CX) on CVHP were observed. In arteriosclerosis group (AS group), the mean flow (Qmean), mean velocity (Vmean), maximal velocity (Vmax) and minimal velocity (Vmin) of the carotid blood flow and cerebrovascular compliance for zero pressure (CO) were significantly decreased (P < 0.05, 0.01), but the values of cerebrovascular peripheral resistance (R) and characteristic impedance (Zc) were significantly increased (P < 0.05 and 0.01), and the value of R showed significant positive correlation with the extent of carotid lesions (P < 0.01). All indexes of CVHP of the Chuanxiong group (CX group) were close to and had no significant difference from those of the normal group (N group) but Qmean, Vmean, Vmin, CO and R were significantly better than those of the AS group (P < 0.05, 0.01). These results showed that CX can effectively improve cerebrovascular hemodynamics.

Animals↗
PubMed1993

Investigation of the mechanism underlying the inhibitory effect of heterologous ras genes in plant cells.

The ras genes from yeast and mammalian cells were fused to plant expression promoters, and introduced into plant cells via Agrobacterium, to study their effect on cell growth and development. All introduced ras genes had a strong inhibitory effect on callus and shoot regeneration from plant tissues. This is consistent with earlier findings that heterologous ras genes were highly lethal to protoplasts following direct DNA uptake. These effects could not be reversed by increasing exogenous or endogenous cytokinin levels. These effects were also independent of the v-Ha-ras mutations in functionally important regions of Ras proteins such as effector-binding and membrane-binding sites. Similarly, co-transformation with the genes encoding the Ras-negative regulators, GTPase-activating protein and neurofibromin did not affect the ras inhibitory effect, indicating that the mechanism of ras inhibition of plant cells is not related to normal ras cellular functions. This conclusion was supported by further studies in which ras gene expression was modified using various promoters and antisense constructs. The introduced ras sequences remained fully inhibitory regardless of which promoters (inducible or tissue-specific) or which orientations (sense or antisense) were tested. This strongly suggests that the ras DNA sequence itself, rather than the Ras protein or ras mRNA, is directly involved in the inhibitory effect. The mechanism underlying this novel phenomenon remains unknown. Introduced ras genes may inhibit plant cell growth by inducing co-suppression of unknown endogenous ras or ras-related genes, thereby leading to the arrest of cell growth.

Animals↗
PubMed1992

Structural alterations in desferrioxamine compatible with iron clearance in animals.

The design, synthesis, and biological evaluation of amideless desferrioxamine analogues are described. The design concept is predicated on the idea that a low molecular weight desferrioxamine analogue would represent a better pharmacophore from which to construct an orally effective or more efficient trihydroxamate than the parent chelator. The study demonstrates that (1) the monohydroxamate units of desferrioxamine must be linked to promote iron clearance, (2) the N-propanoyl-N-pentyl fragments of desferrioxamine can be replaced with smaller, e.g., C-5, methylene units without compromising the analogue's iron-clearing properties, and (3) a delicate balance exists between the molecule's iron-clearing efficiency and its lipophilicity.

Animals↗
PubMed1991

Single amino acid substitution alters T cell determinant selection during antigen processing of Staphylococcus aureus nuclease.

The effect of amino acid residues outside of T cell determinant regions of Staphylococcus aureus nuclease (Nase) on the activation of T cell hybridomas has been investigated. T cell hybridomas derived from BALB/c mice immunized with Nase were screened against a nested set of overlapping synthetic peptides spanning the entire Nase molecule. Five regions of Nase, encompassing residues 1 to 20, 21 to 40, 61 to 80, 101 to 120, and 112 to 130, were found to be the T cell determinants. Region 61 to 80 is the immunodominant site. Mutants of Nase with a single amino acid substitution outside the defined T cell determinants were tested for their ability to stimulate the T cell hybridomas. The substitution of arginine for glutamic acid at residue 43 markedly reduces the antigenic potency of the protein for I-Ed restricted T cell hybridomas, which recognize Nase peptides comprised of residues 21 to 40 (p21-40) or 112 to 130 (p112-130). In contrast, the stimulatory capacity of this mutant for I-Ad restricted T cell hybridomas remains unchanged. Our results suggest that selective regulation of an immune response may be achieved by appropriately mutagenizing protein Ag.

Animals↗
PubMed1989

Impedance of arterial system simulated by viscoelastic t tubes terminated in windkessels.

An improved asymmetric t-tube model of the arterial system is proposed. The model consists of two viscoelastic tubes of differing lengths, each terminated in a modified windkessel with inductance as well as resistance and compliance. Equations for calculating the input impedance of this model are presented. Using typical data from the literature, the model predicts a more realistic impedance modulus and phase than previous models of the circulation. Parametric analysis shows that when peripheral compliances are altered, sharp peaks in the very low frequency portions of the impedance spectra are produced, whereas alterations of either the characteristic impedances or inductances of the terminations have little effect on input impedance. Alteration of the elasticity or relative lengths of the tubes results in shifts in the positions of the maxima and minima akin to those observed experimentally. Change in the viscosity of the walls or of the blood only affects the fluctuations of the impedance spectra without affecting the positions of the maxima and minima. Thus, with this still simple model, very realistic impedance spectra are obtainable. The model provides more insight than previously proposed models into the individual influence of various parameters of the proximal and peripheral vasculature on central hemodynamics.

Arteries↗