Search PubMed⌕ Search

Biomedical subjects

H C Cheung

Publications and source records attributed to H C Cheung.

At least 91 records · Page 5Linked to original sources
PubMed1981

Nanosecond fluorescence spectroscopy of human immunoglobulin A.

The solution properties of five samples of human immunoglobulin A (IgA) were investigated with covalent and hydrophobic fluorescence probes. The immunoglobulins included a secretory IgA and four myeloma proteins of both IgA1 and IgA2 subclasses in the monomeric and dimeric forms. The probe 8-anilinonaphthalene-1-sulfonate (ANS) was found to bind to both monomeric and dimeric IgA with comparable affinity. Pyrenesulfonyl chloride covalently linked to the proteins exhibited multiexponential decays. The decay of ANS complexed to the same proteins showed similar multiple exponential character. The rotational motions of the immunoglobulins were investigated by the nanosecond fluorescence anisotropy decay method. The decay of both probes attached to these proteins was characterized by a fast component followed by a slow component. The rapid component was in the range 14-26 ns for th covalent conjugates and 26-41 ns for the ANS complexes. These results are interpreted in terms of a segmental motion arising from a mass in the range 60 000-100 000 daltons, If the decrease in the anisotropy value at long times is taken as a measure of restricted diffusion of the mobile fragment, the half-angle of a cone within which the fragment traverses may provide a qualitative measure of the extent of flexibility. By this criterion, monomeric and dimeric IgA's of the same subclass appear to be qualitatively similar in flexibility.

Anilino Naphthalenesulfonates↗
PubMed1981

Three sets of actin filaments in sensory cells of the inner ear. Identification and functional orientation determined by gel electrophoresis, immunofluorescence and electron microscopy.

Receptor cells in the ear are mechanically excited through displacement of sensory hairs, stereocilia, in relation to a sub-surface platform, the cuticular plate, into which rootlets of the stereocilia insert. The presence of actin in inner ear sensory organs and receptor cells was established by gel electrophoresis, by labelling with antibodies against actin, and by electron microscopy after decoration with subfragment-1 of myosin. The latter method was used to determine the functional orientation of actin filaments found to be present in the mechanosensitive region of the receptor cells. Actin filaments were demonstrated in the stereocilia and their rootlets, in the cuticular plate and in relation to the zonula adherens surrounding the top of the cell. Filaments which run parallel to the cell surface were found in the cuticular plate and zonula adherens. Some filaments associated with the zonula adherens had a functional orientation opposite to that of more centrally located filaments in the cuticular plate. A structural complex consisting of a solid filament surrounded by actin filaments in hexagonal packing was found in the periphery of the cuticular plate. The possibility is suggested that the central filament is myosin.

Actins↗
PubMed1981

A dopamine receptor model and its application in the design of a new class of rigid pyrrolo[2,3-g]isoquinoline antipsychotics.

A hypothetical model of the interaction of antipsychotic drugs with the dopamine receptor is described. This three-dimensional molecular model has been developed on the basis of plausible intermolecular interactions between pharmacophoric groups of diverse types of antipsychotic drugs and postulated amino acid side chain substituents of the receptor protein. Three essential binding sites (one possibly required for antagonism) and one lipophilic auxiliary binding site are identified. The geometry is defined via the three-dimensional structures of drugs exhibiting receptor activity, including (R)-apomorphine, (+)-dexclamol, and molindone (whose crystal structure has been determined). A new conformationally rigid pyrrolo[2,3-g]isoquinoline derivative has been designed to conform to the receptor model. The compound (+/-)-1 (2,6-dimethyl-3-ethyl-4,4a,5,6,7,8,8a,9-octahydro-4a,8a-trans-1H-pyrrolo[2,3-g] isoquinolin-4-one; Ro 22-1319) exhibits potent antipsychotic-like activity. The activity is stereospecific, residing in the (-) enantiomer, predicted and confirmed by X-ray crystal structure analysis of (-)-1.HCl to have the 4aR,8aR absolute configuration.

Animals↗
PubMed1980

Comparative studies of the binding of ethidium bromide and its photoreactive analogues to nucleic acids by fluorescence and rapid kinetics.

The binding studies of the interaction of ethidium bromide with DNA have been hampered by its reversibility, which prevents direct isolation and thus characterization of the complex. The recent development of photoaffinity labeling has provided a means to circumvent this problem. However, to be useful as a probe for the parent compound, a photosensitive analogue must be shown to interact in vivo and in vitro just as the parent analogue. These studies demonstrate by steady-state and nonosecond fluorescence and stopped-flow kinetics that one of the azido analogues of ethidium, 8-azido-3-amino-5-ethyl-6-phenylphenanthridinium chloride, binds nucleic acids quite similarly to ethidium bromide. The interaction of the other azide, 3,8-diazido-5-ethyl-6-phenyl-phenanthridinium chloride, with DNA is qualitatively different from that of the monoazide and ethidium bromide. These results suggest that the monoazide would serve as an ideal probe for determining the actual target sites of ethidium bromide in vivo and in vitro.

Animals↗
PubMed1980

Fluorescence decay kinetics of pyrene in membrane vesicles.

The fluorescence decay kinetics of pyrene incorporated into artificial and natural membrane vesicles has been studied by pulse fluorimetry. The emission of monomeric pyrene and its excimer embedded in sonicated liposomes prepared from dipalmitoylphosphatidylcholine and a mixture of this phospholipid and dipalmitoylphosphatidylserine follows a multiple exponential decay law at temperatures both below and above their thermal transitions (10--48 degrees C). When pyrene is incorporated into fragmented skeletal sarcoplasmic reticulum vesicles, the emission decay exhibits similar multiple exponential character. The decay of the monomer in the phospholipid vesicles can be adequately described by three exponential terms. The experimental decays observed with both types of vesicles deviate significantly from a previously proposed model in which departure of the decay of pyrene monomer from monoexponentiality is qualitatively related to a time dependence in the diffuslipid vesicles can be adequately described by three exponential terms. The experimental decays observed with both types of vesicles deviate significantly from a previously proposed model in which departure of the decay of pyrene monomer from monoexponentiality is qualitatively related to a time dependence in the diffuslipid vesicles can be adequately described by three exponential terms. The experimental decays observed with both types of vesicles deviate significantly from a previously proposed model in which departure of the decay of pyrene monomer from monoexponentiality is qualitatively related to a time dependence in the diffusion-controlled formation of excimers from ground state and excited monomers. It is suggested that the observed decays are compatible with a reaction scheme involving excited state interaction.

Animals↗
PubMed1980

A membrane abnormality in lymphocytes from diabetic subjects.

The fluorescence properties of the hydrophobic probe 1,6-diphenyl1-1,3,5-hexatriene incorporated in the lymphocytes of 30 diabetic patients and 21 normal control subjects were studied. The mean value of the probe polarization was 0.314 for the control group and 0.294 for the patient group. The difference was significant at p < 0.001. The decreased polarization was correlated with the level of plasma glucose in the patients (p < 0.01). Nanosecond fluorescence results obtained from the lymphocytes of 7 patients and 5 controls indicated that there was no significant difference in the probe lifetimes between the two groups of subjects and suggest that the decreased polarization of the probe in the patient group resulted from a more fluid lipid environment of cell membranes.

Adolescent↗
PubMed1977

Fluorescence depolarization studies on the flexibility of myosin rod.

The single photon counting method has been used to measure the decay of fluorescence polarization anisotropy of myosin rods labeled with extrinsic fluorophores. Rods labeled with 8-anilino-1-naphthalenesulfonate (ANS) or 5-dimethylaminoaphthalene-1-sulfonyl chloride (DNS-Cl) exhibit negative rotational correlation times; the anisotropy increases with time. Possible artifactual causes for the negative decay times are ruled out. It is shown that such curves are to be expected for rigid rods when the fluorophore is bound so that the absorption and emission dipoles each make a small angle with the long axis of the molecule and lie on opposite sides of the rod. At pH 4 and below, rapid decay of the anisotropy (positive correlation times) indicates the presence of a freely bending region in the rod. This is probably the proteolytically sensitive region between light meromyosin and heavy meromyosin subfragment 2. At pH 8, no such free bending is observed, even at temperatures as high as 50 degrees C. From this observation and other physical properties of the rod, we conclude that, at pH 8, the hinge region has considerable resistance to bending. It is more like a spring than a free hinge. The rotational diffusion about the rod axis is faster than would be predicted for a rigid, smooth molecule.

Anilino Naphthalenesulfonates↗
PubMed1977

Dihydroretinoic acids and their derivatives. Synthesis and biological activity.

The syntheses of the ring and four side-chain dihydroretinoic acids and/or their esters, 3-7, are described. The syntheses of several other retinoids containing a substituted aromatic ring are also included. The biological activity of the compounds was evaluated in vivo in a chemically induced mouse skin papilloma test and in vitro in two vitamin A deficient assays. The activity observed for 1a, 1c, and 2a in the former test was partially retained in the dihydro derivatives 4b, 4c, and 6b. Similar results were found in the in vitro assays.

Animals↗
PubMed1977

Actin filaments in sensory hairs of inner ear receptor cells.

Receptor cells in the ear are excited through the bending of sensory hairs which project in a bundle from their surface. The individual stereocilia of a bundle contain filaments about 5 nm in diameter. The identity of these filaments has been investigated in the crista ampullaris of the frog and guinea pig by a technique of decoration with subfragment-1 of myosin (S-1). After demembranation with Triton X-100 and incubation with S-1, "arrowhead" formation was observed along the filaments of the stereocilia and their rootlets and also along filaments in the cuticular plate inside the receptor cell. The distance between attached S-1 was 35 nm and arrowheads pointed in towards the cell soma. It is concluded that the filaments of stereocilia are composed of actin.

Actin Cytoskeleton↗
PubMed1976

Fluorescence studies of 1,N6-ethenoadenosine triphosphate bound to G-actin: the nucleotide base is inaccessible to water.

When 1,N6-ethenoadenosine triphosphate (epsilon-ATP) is free in solution, its fluorescence is collisionally quenched by iodide ion, by methionine, by tryptophan, and by cysteine. None of these quenches the fluorescence of epsilon-ATP bound to G-actin. Thus, the ethenoadenine base is bound in a region of the protein which is inaccessible to collisions with these reagents. Since we have previously shown that the fluorescence of epsilon-ATP is quenched by water, the long lifetime of epsilon-ATP bound to G-actin (36 nsec, vs 27 nsec for epsilon-ATP in water) indicates that the bound nucleotide base is inaccessible to collisional quenching by water molecules.

Actins↗