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Biomedical subjects

M Ge

Publications and source records attributed to M Ge.

At least 19 recordsLinked to original sources
PubMed2001

ADP ribosylation factor 6 binding to phosphatidylinositol 4,5-bisphosphate-containing vesicles creates defects in the bilayer structure: an electron spin resonance study.

The effects of binding of myristoylated ADP ribosylation factor 6 (myr-ARF6), an activator of phospholipase D (PLD), to a model membrane were investigated using an electron spin resonance (ESR) labeling technique. Initial studies were conducted in vesicles composed of 1-palmitoyl-2-oleoyl phosphatidylethanolamine, dipalmitoylphosphatidylcholine, phosphatidylinositol 4,5-biphosphate (PIP(2)), and cholesterol. Recombinant ARF6 binding significantly enhances defects in both the headgroup and acyl-chain regions of the membrane, which are revealed by the emergence of sharp components in the spectra from a headgroup label, 1,2-dipalmitoylphosphatidyl-2,2,6,6-tetramethyl-1-piperidinyloxy-choline (DPPTC), and a chain label, 10PC, after myr-ARF6 binding. Binding of non-myristoylated ARF6 (non-ARF6) shows markedly reduced effects. Interestingly, no change in spectra from DPPTC was observed upon myr-ARF6 binding when PIP(2) in the vesicles was replaced by other negatively charged lipids, including phosphatidylinositol, phosphatidylserine, and phosphatidylglycerol, even when normalized for charge. The production of the sharp peak appears to be a specific event, because another GTP binding protein, CDC42, which binds PIP(2) and activates PLD, fails to induce changes in vesicle structure. These results suggest a previously unappreciated role for ARF in mediating a protein/lipid interaction that produces defects in lipid bilayers. This function may serve as an initial event in destabilizing membrane structure for subsequent membrane fusion or biogenesis of vesicles.

ADP-Ribosylation Factor 6↗
PubMed2001

[The epoxidation of cis-propenylphophonic acid to fosfomycin by Pencillium sp].

One strain of Penicillium sp. F5, found from soil sample, was able to stereo-specific epoxidation of cis-propenylphosphonic acid(PPOH) to fosfomycin[(-)-(1R, 2S)-1, 2-epoxypropylphosphonic acid, FOM] during the cultivation. The product (FOM) was identified by thin layer chromatography and microbiological assay. Under the culture conditions of 28 degrees C pH7.5 and 280 r/min, 0.3% concentration of PPOH, reached a level of 2.2 mg/ml of FoM and the yield was 41%. When the PPOH concentration was 0.6%, the yield was 8%.

Biotransformation↗
PubMed2000

[Experimental study on anti-fatigue effect of shenfu injection on diaphragmatic muscle].

OBJECTIVE: To study the effect of Shenfu injection (SFI) on function of diaphragmatic muscle in rabbits. METHODS: Taking the transdiaphragmatic pressure (Pdi), diaphragmatic electromyogram (EMGdi) and diaphragmatic evoked potential (DEP) as criteria for observation, the diaphragmatic fatigue (DiF) was induced by stimulating bilateral phrenic nerve for 30 minutes. Pdi, EMGdi and DEP induced by stimulation with different frequency (Fc) were recorded before and after treatment. Then the high/low (H/L) frequency ratio and central Fc were calculated and analysed by variance analysis and q test. RESULTS: After administration of 2 ml/kg of SFI, the Pdi, H/L, Fc and amplitude of DEP were markedly increased and latent phase of DEP was shortened by the drug, in comparing with those before treatment, P < 0.05. CONCLUSION: SFI has the effect in antagonizing diaphragmatic fatigue.

Animals↗
PubMed1999

Vancomycin derivatives that inhibit peptidoglycan biosynthesis without binding D-Ala-D-Ala.

Vancomycin is an important drug for the treatment of Gram-positive bacterial infections. Resistance to vancomycin has begun to appear, posing a serious public health threat. Vancomycin analogs containing modified carbohydrates are very active against resistant microorganisms. Results presented here show that these carbohydrate derivatives operate by a different mechanism than vancomycin; moreover, peptide binding is not required for activity. It is proposed that carbohydrate-modified vancomycin compounds are effective against resistant bacteria because they interact directly with bacterial proteins involved in the transglycosylation step of cell wall biosynthesis. These results suggest new strategies for designing glycopeptide antibiotics that overcome bacterial resistance.

Anti-Bacterial Agents↗
PubMed1999

Electron spin resonance characterization of liquid ordered phase of detergent-resistant membranes from RBL-2H3 cells.

The dynamic structure of detergent-resistant membranes (DRMs) isolated from RBL-2H3 cells was characterized using two different acyl chain spin-labeled phospholipids (5PC and 16PC), a headgroup labeled sphingomyelin (SM) analog (SD-Tempo) and a spin-labeled cholestane (CSL). It was shown, by comparison to dispersions of SM, dipalmitoylphosphatidylcholine (DPPC), and DPPC/cholesterol of molar ratio 1, that DRM contains a substantial amount of liquid ordered phase: 1) The rotational diffusion rates (R( perpendicular)) of 16PC in DRM between -5 degrees C and 45 degrees C are nearly the same as those in molar ratio DPPC/Chol = 1 dispersions, and they are substantially greater than R( perpendicular) in pure DPPC dispersions in the gel phase studied above 20 degrees C; 2) The order parameters (S) of 16PC in DRM at temperatures above 4 degrees C are comparable to those in DPPC/Chol = 1 dispersions, but are greater than those in DPPC dispersions in both the gel and liquid crystalline phases. 3) Similarly, R( perpendicular) for 5PC and CSL in DRM is greater than in pure SM dispersions in the gel phase, and S for these labels in DRM is greater than in the SM dispersions in both the gel and liquid crystalline phases. 4) R( perpendicular) of SD-Tempo in DRM is greater than in dispersions of SM in both gel and liquid phases, consistent with the liquid-like mobility in the acyl chain region in DRM. However, S of SD-Tempo in DRM is substantially less than that of this spin label in SM in gel and liquid crystalline phases (in absolute values), indicating that the headgroup region in DRMs is less ordered than in pure SM. These results support the hypothesis that plasma membranes contain DRM domains with a liquid ordered phase that may coexist with a liquid crystalline phase. There also appears to be a coexisting region in DRMs in which the chain labels 16PC and 5PC are found to cluster. We suggest that other biological membranes containing high concentrations of cholesterol also contain a liquid ordered phase.

1,2-Dipalmitoylphosphatidylcholine↗
PubMed1999

Electron-spin resonance study of aggregation of gramicidin in dipalmitoylphosphatidylcholine bilayers and hydrophobic mismatch.

The effect of aggregation of gramicidin A' (GA) on the phase structure of dipalmitoylphosphatidylcholine (DPPC) multilamellar vesicles was studied by cw-ESR using a chain-labeled lipid (16PC) at temperatures between 30 degrees and 45 degreesC that span the main phase transition of DPPC. Boundary lipids were observed only in dispersions with GA/DPPC molar ratios >1:15, where GA aggregates. Detailed fits by nonlinear least squares (NLLS) methods are consistent with the boundary lipid being characterized by a large negative order parameter ( approximately -0.4), indicative of a dynamic bending of the end of the acyl chain, and a substantially reduced motion, about an order of magnitude slower than that of the bulk lipid. The NLLS analysis compares favorably with a recent two-dimensional Fourier transform ESR study on DPPC/GA vesicles, which accurately discerned the bulk lipid. The detailed ESR observables are discussed in terms of the ordering effect of GA at low concentration of GA, the dissociation of the GA channel and the dynamic bending of the end chain segment of boundary lipid at high concentration of GA, and of HII phase formation induced by GA. It is suggested that these phenomena can be interpreted in terms of the combined effects of partial dehydration of the lipid headgroup by the GA and of the hydrophobic mismatch between GA and DPPC molecules. Substantial hysteresis is observed for heating versus cooling cycles, but only for a GA/DPPC molar ratio >1:15. This is consistent with the aggregation of GA molecules at high concentrations.

1,2-Dipalmitoylphosphatidylcholine↗
PubMed1998

[Interference of human processed pseudogene and corresponding counter-measures in reverse transcriptase-polymerase chain reaction].

OBJECTIVE: This study aimed to set up an effective method to find the interference of processed pseudogene and overcome it in RT-PCR. METHODS: Using RT-PCR methods, the authors amplified the cytokeratin 19 cDNA or DNA sequence in human lung squamous cell carcinoma samples. RESULTS: They could find the influence of pseudogene through performing genomic DNA and nonreversed transcribed RNA controls. By digesting the extracted RNA sample with RNase-free DNase or regulating the annealing temperature based on mismatched primers, they could effectively eliminate the interference. CONCLUSION: The presence of processed pseudogene usually interferes in the experimental protocol in RT-PCR. This problem can be resolved with the method aforementioned.

Carcinoma, Squamous Cell↗
PubMed1998

Polarity profiles in oriented and dispersed phosphatidylcholine bilayers are different: an electron spin resonance study.

A novel method was utilized to accurately measure the z- component of the nuclear hyperfine interaction tensor, Azz, of a chain-labeled lipid, 16PC, and a headgroup-labeled lipid, dipalmitoylphosphatidyl-tempocholine (DPPTC), in macroscopically oriented dipalmitoylphosphatidylcholine (DPPC) and dimyristoylphosphatidylcholine (DMPC) membranes, which were compared with the Azz values of the two labels in dispersions of the same lipids in the gel phase. We found that the Azz values of 16PC (DPPTC) in the oriented DPPC and DMPC bilayers are approximately 1 Gauss smaller (greater) than in the corresponding dispersions. These results indicate that the headgroup region is more polar in macroscopically oriented bilayers than in dispersions, whereas in the chain region, the order in polarity is reversed. This is consistent with previous results on partial molar volumes in the liquid-crystal phase. Differences in the morphology of the macroscopically oriented and dispersed bilayers, which might be responsible, are discussed. Nonlinear least-squares fits of the electron spin resonance spectra of DPPTC in DPPC show that there is a substantial orienting potential in the headgroup region of dispersions that is lipid phase dependent. However, in oriented membrane samples hydrated in 100% relative humidity, this orienting potential is very weak.

1,2-Dipalmitoylphosphatidylcholine↗
PubMed1997

Polyvalent binding to carbohydrates immobilized on an insoluble resin.

Numerous studies have established that polyvalency is a critical feature of cell surface carbohydrate recognition. Nevertheless, carbohydrate-protein interactions are typically evaluated by using assays that focus on the behavior of monovalent carbohydrate ligands in solution. It has generally been assumed that the relative affinities of monovalent carbohydrate ligands in solution correlate with their polyvalent avidities. In this paper we show that carbohydrate ligands synthesized directly on TentaGel beads interact with carbohydrate-binding proteins in a polyvalent manner. The carbohydrate-derivatized beads can, therefore, be used as model systems for cell surfaces to evaluate polyvalent carbohydrate-protein interactions. By using a combinatorial approach to synthesize solid-phase libraries of polyvalent carbohydrates, one can rapidly address key issues in the area of cell surface carbohydrate recognition. For example, studies reported herein demonstrate that there is an unanticipated degree of specificity in recognition processes involving polyvalent carbohydrates. However, the correlation between polyvalent avidities and solution affinities is poor. Apparently, the presentation of carbohydrates on the polymer surface has a profound influence on the interaction of the ligand with the protein receptor. These findings have implications for how carbohydrates function as recognition signals in nature, as well as for how polyvalent carbohydrate-protein interactions should be studied.

Carbohydrate Metabolism↗
PubMed1997

[Relationship between reference value (Wintrobe) of Chinese healthy female hematocrit and geographical factors].

To provide a basis for uniting the reference value standard (Wintrobe) of Chinese healthy female hematocrit, a study has been made on the relationship between the reference value of 22135 cases of Chinese female hematocrit and five geographical factors in China's 436 areas, which were determined by the method of Wintrobe. It is found that altitude is the main factor affecting the reference value (Wintrobe) of Chinese healthy female hematocrit. As the altitude increases gradually, the reference value (Wintrobe) of Chinese healthy female hematocrit also increases. For applying the method of mathematical regression analysis, a multivariate regression equation is formulated. In case geographical index values are obtained in an area, the reference value (Wintrobe) of Chinese healthy female heamtocrit for this area can be reckoned using the regression equation. Furthermore, according to the similarity of the reference values (Wintrobe) of Chinese healthy female hematocrit, China can be divided into six regions: Qinghai-Xizang region, southwest region, northwest region, southeast region, north region and northeast region.

Altitude↗
PubMed1996

Parallel synthesis and screening of a solid phase carbohydrate library.

A solid phase carbohydrate library was synthesized and screened against Bauhinia purpurea lectin. The library, which contains approximately 1300 di- and trisaccharides, was synthesized with chemical encoding on TentaGel resin so that each bead contained a single carbohydrate. Two ligands that bind more tightly to the lectin than Gal-beta-1,3-GalNAc (the known ligand) have been identified. The strategy outlined can be used to identify carbohydrate-based ligands for any receptor; however, because the derivatized beads mimic the polyvalent presentation of cell surface carbohydrates, the screen may prove especially valuable for discovering new compounds that bind to proteins participating in cell adhesion.

Acylation↗
PubMed1995

[Effect of shengmai san on diaphragmatic function in rabbits].

After stimulation of the bilateral phrenic nerves of the rabbits, the effect of Shengmai San (SMS) on their normal function and the diaphragmatic fatigue was observed with the measuring of diaphragm evoked potential (DEP), and the analysis of the power spectrum of diaphragmatic electromyogram (EMGdi) at spontaneous breathing. The results were as follows: (1) After the administration of 2 ml/kg of SMS, amplitude of DEP, central frequency, and the high/low frequency ratio were markedly increased. (2) Injecting SMS in 2 ml/kg in 30 minutes before injury could protect significantly against diaphragmatic fatigue following electrical stimulation of the phrenic nerves. (3) Injecting SMS in 2 ml/kg after fatigue could enhance the recovery of the diaphragmatic fatigue.

Animals↗
PubMed1994

ESR studies of spin-labeled membranes aligned by isopotential spin-dry ultracentrifugation: lipid-protein interactions.

Electron spin resonance (ESR) studies have been performed on spin-labeled model membranes aligned using the isopotential spin-dry ultracentrifugation (ISDU) method of Clark and Rothschild. This method relies on sedimentation of the membrane fragments onto a gravitational isopotential surface with simultaneous evaporation of the solvent in a vacuum ultracentrifuge to promote alignment. The degree of alignment obtainable using ISDU, as monitored by ESR measurements of molecular ordering for both lipid (16-PC) and cholestane spin labels (CSL), in dipalmitoylphosphatidylcholine (DPPC) model membranes compares favorably with that obtainable by pressure-annealing. The much gentler conditions under which membranes may be aligned by ISDU greatly extends the range of macroscopically aligned membrane samples that may be investigated by ESR. We report the first ESR study of an integral membrane protein, bacteriorhodopsin (BR) in well-aligned multilayers. We have also examined ISDU-aligned DPPC multilayers incorporating a short peptide gramicidin A' (GA), with higher water content than previously studied. 0.24 mol% BR/DPPC membranes with CSL probe show two distinct components, primarily in the gel phase, which can be attributed to bulk and boundary regions of the bilayer. The boundary regions show sharply decreased molecular ordering and spectral effects comparable to those observed from 2 mol% GA/DPPC membranes. The boundary regions for both BR and GA also exhibit increased fluidity as monitored by the rotational diffusion rates. The high water content of the GA/DPPC membranes reduces the disordering effect as evidenced by the reduced populations of the disordered components. The ESR spectra obtained slightly below the main phase transition of DPPC from both the peptide- and protein-containing membranes reveals a new component with increased ordering of the lipids associated with the peptide or protein. This increase coincides with a broad endothermic peak in the DSC, suggesting a disaggregation of both the peptide and the protein before the main phase transition of the lipid. Detailed simulations of the multicomponent ESR spectra have been performed by the latest nonlinear least-squares methods, which have helped to clarify the spectral interpretations. It is found that the simulations of ESR spectra from CSL in the gel phase for all the lipid membranes studied could be significantly improved by utilizing a model with CSL molecules existing as both hydrogen-bonded to the bilayer interface and non-hydrogen-bonded within the bilayer.

1,2-Dipalmitoylphosphatidylcholine↗
PubMed1994

250-GHz electron spin resonance studies of polarity gradients along the aliphatic chains in phospholipid membranes.

Rigid-limit 250-GHz electron spin resonance (FIR-ESR) spectra have been studied for a series of phosphatidylcholine spin labels (n-PC, where n = 5, 7, 10, 12, 16) in pure lipid dispersions of dipalmitoylphosphatidylcholine (DPPC) and 1-palmitoyl-2-oleoylphosphatidylcholine (POPC), as well as dispersions of DPPC containing the peptide gramicidin A (GA) in a 1:1 molar ratio. The enhanced g-tensor resolution of 250-GHz ESR for these spin labels permitted a careful study of the nitroxide g-tensor as a function of spin probe location and membrane composition. In particular, as the spin label is displaced from the polar head group, Azz decreases and gxx increases as they assume values typical of a nonpolar environment, appropriate for the hydrophobic alkyl chains in the case of pure lipid dispersions. The field shifts of spectral features due to changes in gxx are an order of magnitude larger than those from changes in Azz. The magnetic tensor parameters measured in the presence of GA were characteristic of a polar environment and showed only a very weak dependence of Azz and gxx on label position. These results demonstrate the significant influence of GA on the local polarity along the lipid molecule, and may reflect increased penetration of water into the alkyl chain region of the lipid in the presence of GA. The spectra from the pure lipid dispersions also exhibit a broad background signal that is most significant for 7-, 10-, and 12-PC, and is more pronounced in DPPC than in POPC. It is attributed to spin probe aggregation yielding spin exchange narrowing. The addition of GA to DPPC essentially suppressed the broad background signal observed in pure DPPC dispersions.

1,2-Dipalmitoylphosphatidylcholine↗
PubMed1994

An electron spin resonance study of interactions between phosphatidylcholine and phosphatidylserine in oriented membranes.

A detailed electron spin resonance (ESR) study of mixtures of 1-palmitoyl-2-oleoyl-phosphatidylcholine (POPC) and phosphatidylserine (POPS) in oriented multilayers in the liquid crystalline phase is reported with the purpose of characterizing the effects of headgroup mixing on the structural and dynamical properties of the acyl chains. These studies were performed over a range of blends of POPC and POPS and temperatures, utilizing the spin-labeled lipids 16-phosphatidylcholine and 5-phosphatidylcholine as well as cholestane (CSL). The ESR spectra were analyzed by nonlinear least-squares fitting using detailed spectral simulations. Whereas CSL shows almost no variation in ordering and rotational dynamics versus mole fraction POPS, (i.e. XPS), and 5-PC shows small effects, the weakly ordered end-chain labeled 16-PC shows large relative effects, such that the orientational order parameter, S is at a minimum for XPS = 0.5 where it is about one-third the value observed for XPS = 0 and 1. This is directly reflected in the ESR spectrum as a substantial variation in the hyperfine splitting with XPS. The least-squares analysis also shows a reduction in rotational diffusion coefficient, R perpendicular by a fractor of 2 for XPS = 0.5 and permits the estimation of S2, the ordering parameter representing deviations from cylindrically symmetric alignment. These results are contrasted with 2H NMR studies which were insensitive to effects of mixing headgroups on the acyl chains. The ESR results are consistent with a somewhat increased disorder in the end-chain region as well as a small amount of chain tilting upon mixing POPC and POPS. They demonstrate the high sensitivity of ESR to subtle effects in chain ordering and dynamics.

Biophysical Phenomena↗