Biomedical subjects

Chun Zhou

Publications and source records attributed to Chun Zhou.

29 records · Page 2Linked to original sources

PubMed2004

In vitro flavon-3-ol oxidation mediated by a B ring hydroxylation pattern.

Flavonols are potent naturally occurring antioxidants. Chemical oxidation reactions in combination with modern spectroscopic techniques have been employed to identify oxidized flavonoid products. Although many oxidized derivatives have been generated from commercially available starting materials, few studies have developed a sequence of flavonoid substrates with a particular hydroxylation pattern to probe the mechanism of flavonoid oxidation. Here, we use AIBN (2,2'-azobisisobutyronitrile) in combination with a series of hydroxylated flavonols to probe the mechanism of flavonoid dimer formation and the role of singly or doubly oxidized species in generating and promoting oxidized flavonoid products. 3-Methoxyquercetin (3-hydroxyl group blocked) and luteolin (lack of 3-hydroxyl) were reacted with AIBN alone or with a second flavonol to serve as a C-3 hydroxyl donor to examine the mechanism of dimer formation. 3-Hydroxyflavones with increasing hydroxyl substitutions in the B ring were also reacted with AIBN in the presence or absence of an external nucleophile to examine the role of various hydroxyls in the formation of a carbocation intermediate via a doubly oxidized species. The presence of a free C-3 hydroxyl, coupled with a B ring ortho hydroxy unit, appears essential for dimer formation. An increase in the number of hydroxyls in the B ring facilitates products generated from a doubly oxidized species.

Chromatography, Liquid↗

PubMed2004

Cloning and characterization of a human cDNA ACAD10 mapped to chromosome 12q24.1.

Mitochondrial fatty acid beta-oxidation is an important energy resource for many mammal tissues. Acyl-CoA dehydrogenases (ACADs) are a family of flavoproteins that are involved in the beta-oxidation of the fatty acyl-CoA derivatives. Deficiency of these ACADs can cause metabolic disorders including muscle fatigue, hypoglycaemia, hepatic lipidosis and so on. By large scale sequencing, we identified a cDNA sequence of 3960 base pairs with a typical acyl-CoA dehydrogenase function domain. RT-PCR result shows that it is widely expressed in human tissues, especially high in liver, kidney, pancreas and spleen. It is hypothesized that this is a novel member of ACADs family.

Acyl-CoA Dehydrogenase↗

PubMed2003

Polarographic behavior of Co(II)-BSA or -HSA complex in the presence of a guanidine modifier.

An extremely sensitive adsorptive wave of BSA at about -1.73 V (vs SCE) has been obtained in the solution containing 8 x 10(-)(7) mol/L CoCl(2), 0.2 mol/L guanidine hydrochloride, and 0.2 mol/L NaOH by using single-sweep polarography. The interaction of BSA with guanidine in an alkaline solution results in its Co(II) complex with a positive excess charge. Thus, the complex is strongly adsorbed by the DME as a result of static electrical attraction. The adsorption efficiently accumulates the electrochemical active complex of Co(II)-BSA onto the DME. In the following potential scan, the complex produces a sensitive adsorptive reduction peak, which can be used to determine low-level BSA. In the absence of guanidine, the complex of Co(II)-BSA with a negative excess charge is repulsed by the DME. The reduction current is very small. The peak current depends on both BSA and Co(II) ion concentrations. HSA is similar to BSA in polarographic behavior. At the optimal conditions, the peak height is linearly proportional to the BSA or HSA concentration in the range of 0.005-20 mg/L (correlation coefficient 0.999). The detection limit for BSA or HSA is 0.002 mg/L. Lysozyme, common amino acids, and metal ions have no interference with the protein determination. The new method could be useful in protein studies.

Adsorption↗

PubMed2003

Roles of phosphoinositides and of Spo14p (phospholipase D)-generated phosphatidic acid during yeast sporulation.

During yeast sporulation, internal membrane synthesis ensures that each haploid nucleus is packaged into a spore. Prospore membrane formation requires Spo14p, a phosphatidylinositol 4,5-bisphosphate [PtdIns(4,5)P2]-stimulated phospholipase D (PLD), which hydrolyzes phosphatidylcholine (PtdCho) to phosphatidic acid (PtdOH) and choline. We found that both meiosis and spore formation also require the phosphatidylinositol (PtdIns)/PtdCho transport protein Sec14p. Specific ablation of the PtdIns transport activity of Sec14p was sufficient to impair spore formation but not meiosis. Overexpression of Pik1p, a PtdIns 4-kinase, suppressed the sec14-1 meiosis and spore formation defects; conversely, pik1-ts diploids failed to undergo meiosis and spore formation. The PtdIns(4)P 5-kinase, Mss4p, also is essential for spore formation. Use of phosphoinositide-specific GFP-PH domain reporters confirmed that PtdIns(4,5)P2 is enriched in prospore membranes. sec14, pik1, and mss4 mutants displayed decreased Spo14p PLD activity, whereas absence of Spo14p did not affect phosphoinositide levels in vivo, suggesting that formation of PtdIns(4,5)P2 is important for Spo14p activity. Spo14p-generated PtdOH appears to have an essential role in sporulation, because treatment of cells with 1-butanol, which supports Spo14p-catalyzed PtdCho breakdown but leads to production of Cho and Ptd-butanol, blocks spore formation at concentrations where the inert isomer, 2-butanol, has little effect. Thus, rather than a role for PtdOH in stimulating PtdIns(4,5)P2 formation, our findings indicate that during sporulation, Spo14p-mediated PtdOH production functions downstream of Sec14p-, Pik1p-, and Mss4p-dependent PtdIns(4,5)P2 synthesis.

1-Butanol↗

PubMed2003

CXCR4 regulates interneuron migration in the developing neocortex.

The chemotactic factors directing interneuron migration during cerebrocortical development are essentially unknown. Here we identify the CXC chemokine receptor 4 (CXCR4) in interneuron precursors migrating from the basal forebrain to the neocortex and demonstrate that stromal cell-derived factor-1 (SDF-1) is a potent chemoattractant for isolated striatal precursors. In addition, we show that CXCR4 is present in early generated Cajal-Retzius cells of the cortical marginal zone. In mice with a null mutation in CXCR4 or SDF-1, interneurons were severely underrepresented in the superficial layers and ectopically placed in the deep layers of the neocortex. In contrast, the submeningeal positioning of Cajal-Retzius cells was unaffected. Thus, our findings suggest that SDF-1, which is highly expressed in the embryonic leptomeninx, selectively regulates migration and layer-specific integration of CXCR4-expressing interneurons during neocortical development.

Animals↗

PubMed2003

Density functional theory calculations for resveratrol.

The calculations based on the density functional theory (DFT) have been used to study the structure-activity of resveratrol in the chain reaction of autooxidation. According to the geometry obtained by using a B3LYP/6-31G**, the HOMO, LUMO of resveratrol and the spin density, the single electron distribution of the 4'- and 5-radical of resveratrol were calculated, it was found that resveratrol is a potential antioxidant. The 4'-hydroxyl group of resveratrol is more reactive than 3- and 5-positions because of the resonance effects. The dominant structure of the resveratrol radicals is a semiquinone structure which determines the stability of radicals, and the unpaired electron is mainly distributed to the O-atom and its ortho and para positions. The antioxidant activity of resveratrol is related to the spin density and the unpaired electron distribution of the O-atom.

Antioxidants↗

PubMed2002

Sequential transition States and the valley-ridge inflection point in the formation of a semibullvalene.

[structure: see text] Two sequential transition states are calculated at the B3LYP/6-31G(d,p) level for the deazetization of 3b. The intrinsic reaction coordinate for loss of nitrogen passes through a transition state and then a valley-ridge inflection point and ultimately leads to the transition state for the Cope rearrangement of semibullvalene 4b. The energetic and geometrical consequences are discussed.

Journal Article↗

PubMed2002

A density functional theory study clarifying the reactions of conjugated ketenes with formaldimine. A plethora of pericyclic and pseudopericyclic pathways.

The reactions of vinylketene (1a), imidoylketene (1b), and formylketene (1c) with formaldimine (2) were studied at the B3LYP/6-31G* level. For the cycloadditions of these conjugated ketenes with 2, several possible pathways to both [4 + 2] and [2 + 2] products were examined. The lowest energy [2 + 2] pathways are, in most cases, calculated to be stepwise, forming the products via rate-determining conrotatory electrocyclization of zwitterionic intermediates. However, concerted transition structures analogous to the ketene plus ethene [2 + 2] cycloaddition reaction were also located; the existence of multiple transition states offers a resolution to a long-standing controversy regarding the mechanism of ketene plus imine cycloadditions. Both stepwise and concerted [4 + 2] pathways were calculated for 2b and for 2c; both these pathways are pseudopericyclic. The inherently low barriers associated with pseudopericyclic transition states provide an explanation of the experimental preference for [4 + 2] cycloadditions of alpha-oxoketenes and predict [4 + 2] cycloadditions should also be favored for imidoylketenes. For a vinylketene constrained to a Z-geometry, the concerted [4 + 2] cycloaddition is also predicted to be the lowest energy pathway. An explanation is offered for the unusual thermal equilibration from a six-membered ring (3d) to a four-membered ring (4d) observed by Sato et al. Transition structures for facile pseudopericyclic 1,3- and 1,5-hydrogen shifts in the zwitterions were also calculated.

Journal Article↗

PubMed2002

Telomere elongation (Tel), a new mutation in Drosophila melanogaster that produces long telomeres.

In most eukaryotes telomeres are extended by telomerase. Drosophila melanogaster, however, lacks telomerase, and telomere-specific non-LTR retrotransposons, HeT-A and TART, transpose specifically to chromosome ends. A Drosophila strain, Gaiano, that has long telomeres has been identified. We extracted the major Gaiano chromosomes into an Oregon-R genetic background and examined the resulting stocks after 60 generations. In situ hybridization using HeT-A and TART sequences showed that, in stocks carrying either the X or the second chromosome from Gaiano, only the Gaiano-derived chromosomes display long telomeres. However, in stocks carrying the Gaiano third chromosome, all telomeres are substantially elongated, indicating that the Gaiano chromosome 3 carries a factor that increases HeT-A and TART addition to the telomeres. We show that this factor, termed Telomere elongation (Tel), is dominant and localizes as a single unit to 69 on the genetic map. The long telomeres tend to associate with each other in both polytene and mitotic cells. These associations depend on telomere length rather than the presence of Tel. Associations between metaphase chromosomes are resolved during anaphase, suggesting that they are mediated by either proteinaceous links or DNA hydrogen bonding, rather than covalent DNA-DNA bonds.

Anaphase↗

PubMed2002

Differential regulation of Saccharomyces cerevisiae phospholipase D in sporulation and Sec14-independent secretion.

Saccharomyces cerevisiae Spo14, a phosphatidylcholine-specific, phosphatidylinositol (4,5) bisphosphate-activated phospholipase D (PLD), is essential for meiosis and spore formation. Spo14 is also required for secretion in the absence of the phosphatidylinositol/phosphatidylcholine transfer protein Sec14 (i.e., Sec14-independent secretion). In sporulating cells Spo14 is phosphorylated and relocalized within the cell. In contrast, Spo14 does not relocalize and is not phosphorylated in Sec14-independent secretion. Analysis of a partially phosphatidylinositol (4,5) bisphosphate-activated Spo14 mutant, spo14(R894G), revealed that Spo14 function in Sec14-independent secretion, unlike the situation in meiosis, requires fully stimulated PLD activity. Consistent with the differential regulation of Spo14 function during sporulation and secretion, we isolated a mutant allele, spo14-S251P, the product of which is improperly phosphorylated and fails to relocalize and rescue the sporulation phenotype of homozygous spo14 diploids, but supports Sec14-independent secretion. Furthermore, we show that the N-terminal domain of Spo14 is both phosphorylated and sufficient for prospore membrane localization during sporulation. These data indicate that Spo14 phosphorylation and relocalization are essential for the process of sporulation, but dispensable for Sec14-independent secretion. Finally, we demonstrate that Spo14 phosphorylation and relocalization are initiated by nitrogen and glucose limitation and occur independently of the process of meiosis.

Carrier Proteins↗

PubMedDate not supplied

A human single-chain Fv intrabody preferentially targets amino-terminal Huntingtin's fragments in striatal models of Huntington's disease.

Amino-terminal fragments of huntingtin (htt) appear to result from proteolytic processing of the full-length protein in Huntington's disease (HD), and fragments containing pathological expansions of polyglutamine elicit toxicity in model systems. Such fragments are sequestered into insoluble aggregates, which may initially serve a cellular protective mechanism, while soluble fragments and/or oligomers may be a more acute toxic species. Agents which enhance mutant htt clearance have shown therapeutic potential in animal models of HD. Here, we present the first evidence of an htt-specific single-chain Fv intrabody (C4) that selectively targets the soluble fraction of amino-terminal htt fragments. Our findings suggest that the C4 intrabody binds weakly, but does not alter the levels of endogenous, full-length htt. C4 appears to decrease the steady-state levels of amino-terminal htt fragments by binding to non-aggregated, but not aggregated, htt species. Intrabodies may be used as potential curative agents, and as drug discovery tools, for HD and other misfolded protein disorders.

Animals↗