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Biomedical subjects

C Chen

Publications and source records attributed to C Chen.

At least 1,261 records · Page 70Linked to original sources
PubMed1984

A study of the small spherical high density lipoproteins of patients afflicted with familial lecithin: cholesterol acyltransferase deficiency.

We studied the effects of the lecithin:cholesterol acyltransferase reaction on the size and composition of the small spherical high density lipoproteins of patients afflicted with familial lecithin:cholesterol acyltransferase deficiency. We isolated these lipoproteins by preparative ultracentrifugation and rate zonal ultracentrifugation, determined their diameter by gradient gel electrophoresis, and then calculated their composition by relating measurements of their lipid and apolipoprotein content to particle volume. Our results revealed lipoprotein particles 6.0-6.2 nm in diameter that contained approximately 2 molecules of apolipoprotein A-I, 37-38 molecules of phospholipid, 3-9 molecules of unesterified cholesterol, 1-2 molecules of cholesteryl ester, and 1-2 molecules of triacylglycerol. Upon being incubated with lecithin:cholesterol acyltransferase and a source of additional unesterified cholesterol, these lipoproteins increased in content of total cholesterol and in particle size to form discrete lipoprotein products 6.6-8.6 nm in diameter. The increase in size occurred despite a net decrease in product unesterified cholesterol and phospholipid and though the net change in total lipid volume was small. Moreover, specific product lipoproteins, isolated by rate zonal ultracentrifugation, contained an increased amount of apolipoprotein A-I. These results seem best explained by a process involving lecithin:cholesterol acyltransferase-induced particle rearrangement reactions. The possibility that a similar process normally occurs in vivo deserves to be explored.

Electrophoresis, Polyacrylamide Gel↗
PubMed1983

B to Z transition of double-stranded poly[deoxyguanylyl(3'-5')-5-methyldeoxycytidine] in solution by phosphorus-31 and carbon-13 nuclear magnetic resonance spectroscopy.

The B to Z transition of poly(dG-m5dC) . poly(dG-m5dC) has been monitored by 31P nuclear magnetic resonance (NMR) spectroscopy as a function of concentration of several salts. In 5 mM Tris- [tris(hydroxymethyl)amino-methane] HCl buffer two peaks of equal area (0.27 ppm separation) are observed at -4.2 ppm (upfield from trimethyl phosphate), indicating an alternating (right-handed) B conformation. Upon addition of NaCl, CsF, MgCl2, or Co(NH3)6Cl3, a signal arises at -3 ppm that is characteristic of the left-handed Z form. This signal is half of a doublet (1.3-2.1 ppm separation) and is tentatively assigned to the tg+ phosphodiester conformation in the Z form. The midpoints of the cooperative B to Z transitions with these salts are in good agreement with the values reported from circular dichroism (CD) studies for this copolymer. The 13C NMR spectra at natural abundance of poly(dG-m5dC) . poly(dG-m5dC) in the alternating B conformation in low salt show a broad resonance for the C2' and no clear resonance for the C3'. This is in contrast to the alternating B form of poly(dA-dT) . poly(dA-dT) under similar conditions, which exhibits a well-resolved doublet for both C2' and C3' that is presumed to derive from alternating C2'-endo and C3'-endo deoxyribose conformations. In the 13C NMR spectrum of the Z form of poly(dG-m5dC) . poly(dG-m5dC), two major peaks are observed for the C2', which may also indicate an alternating sugar conformation.

Magnetic Resonance Spectroscopy↗
PubMed1983

Cellular Fractionation of Chlamydomonas reinhardii with Emphasis on the Isolation of the Chloroplast.

A method for cellular fractionation of Chlamydomonas reinhardii, SAG 11-32/b, and isolation of intact chloroplasts from synchronized cells of the alga is described. The procedure for cell fractionation comprises essentially four steps: (1) protoplast production with autolysine; (2) lysis of the protoplasts with digitonin; (3) aggregation of broken protoplasts; and (4) separation of organelles by differential centrifugations.Replacing the differential centrifugations (step 4) by Percoll cushion centrifugations yields intact chloroplasts. Starting with 100 milliliters of an algal culture containing 3000 micrograms chlorophyll, intact chloroplasts with 100 to 200 micrograms of chlorophyll can be isolated. Envelope integrity is about 90% (ferricyanide assay). Examination of the chloroplasts by electron microscopy and marker enzyme activities indicated some mitochondrial and cytoplasmic contamination.

Journal Article↗
PubMed1983

Photosynthetic Properties of Chloroplasts from Chlamydomonas reinhardii.

Chloroplasts isolated from synchronous cultures of the unicellular green alga Chlamydomonas reinhardii, SAG 11-32/b (-), fix CO(2) at rates between 25 and 50 micromoles per milligram chlorophyll per hour. The upper value is approximately half of the rate of the intact cell.During storage in the dark on ice, the chloroplast preparation loses 30 to 50% of its CO(2) fixing capability per hour. Under reducing conditions (+ 1 millimolar dithiothreitol), this loss of activity is about twice as fast. The same reducing conditions stimulate CO(2) fixation in the light.High concentrations of inorganic phosphate (>2 millimolar) inhibit CO(2) fixation. This inhibition is overcome by the addition of glycerate 3-phosphate. It is concluded that chloroplasts from C. reinhardii possess a higher plant type phosphate translocator. With respect to dependency upon light intensity, pH and Mg(2+) concentration, the results were similar to that reported for chloroplasts from higher plants. However, in contrast to higher plant chloroplasts, maximum CO(2) fixation is observed at the relatively low osmotic concentration of 0.12 molar mannitol in the reaction buffer.

Journal Article↗
PubMed1983

Stromal acidification mediates in vivo water stress inhibition of nonstomatal-controlled photosynthesis.

Stromal acidification has been reported to mediate reduced osmotic potential (psi(pi)) effects on photosynthesis in the isolated spinach chloroplast (Berkowitz, Gibbs 1983 Plant Physiol 72: 1100-1109). To determine if stromal acidification mediates osmotic dehydration inhibition of photosynthesis in vivo, the effects of a weak base (NH(4)Cl), which raises stromal pH, on CO(2) fixation of vacuum-infiltrated spinach leaf slices, Chlamydomonas reinhardii cells and Aphanocapsa 6308 cells under isotonic and dehydrating conditions were investigated. Five millimolar NH(4)Cl stimulated spinach leaf slice CO(2) fixation by 43% under stress (0.67 molar sorbitol) conditions, and had little effect on fixation under isotonic (0.33 molar sorbitol) conditions. Chlamydomonas cells were found to be more sensitive to reduced psi(pi) than spinach leaf slices. CO(2) fixation in the cells of the green alga Chlamydomonas reinhardii was 99 and 17 micromoles per milligram chlorophyll per hour, respectively, at 0.1 molar mannitol and 0.28 molar mannitol. Five millimolar NH(4)Cl stimulated CO(2) fixation of Chlamydomonas cells by 147% under stress (0.28 molar mannitol) conditions. Aphanocapsa 6308 cells (blue-green alga) were also found to be sensitive to reduced psi(pi), and inhibitions in photosynthesis were partially reversed by NH(4)Cl. These data indicate that in vivo water stress inhibition of photosynthesis is facilitated by stromal acidification, and that this inhibition can be at least partially reversed in situ.

Journal Article↗
PubMed1982

Prostate alpha-protein. Isolation and characterization of the polypeptide components and cholesterol binding.

alpha-Protein, a major glycoprotein in the cytosol fraction of rat ventral prostate, has a molecular weight of about 50,000 and can be dissociated, by sodium dodecyl sulfate, into two different subunits (A and B). alpha-Protein has three different polypeptide components with apparent molecular weights of 10,000 (I), 14,000 (II), and 15,000 (III). These components were purified to homogeneity and their amino acid compositions were determined. Subunit A is composed of Components I and III, whereas subunit B is composed of Components II and III. Carbohydrate was detectable only on Component III. Component III isolated from subunit A and Component III isolated from subunit B appear to be identical. The purified alpha-protein contains 0.7-1 mol of cholesterol/mol of protein. If cholesterol was removed by acetone, about 1 mol of 5 alpha-dihydrotestosterone or pregnenolone could bind to 1 mol of alpha-protein. In the presence of 2 mM ZnCl2, alpha-protein can form dimers and tetramers. In cell-free systems, alpha-protein can inhibit binding of the androgen-receptor complex to nuclear chromatin and also can promote the release of the complex already bound to chromatin. This effect is due to polypeptide Component I.

Amino Acids↗
PubMed1982

Prostate alpha-protein. Complete amino acid sequence of the component that inhibits nuclear retention of the androgen-receptor complex.

The amino acid sequence of Component I of alpha-protein, a glutamic acid-rich protein, is presented. Component I is a single chain polypeptide which consists of 88 amino acid residues with a molecular weight of 10,191. Component I has the amino acid composition Lys6, His, Arg2, Cys3, Asp5, Asn2, Thr3, Ser4, Glu13, Gln3, Pro3, Gly2, Ala6, Val9, Met4, Ile4, Leu8, Tyr6, Phe3, Trp, with serine and asparagine as NH2(-) and COOH-terminal amino acids, respectively. Automated sequences analysis of the whole protein, as well as characterization of the peptides obtained from trypsin, chymotrypsin, and staphylococcal protease digestion and cyanogen bromide treatment, led to the elucidation of the complete primary structure of this protein.

Amino Acid Sequence↗
PubMed1982

Close apposition of muscle cells in the longitudinal bands of the body wall of a holothurian, Isostichopus badionotus.

Electron microscopy reveals that sarcolemmata of adjacent muscle cells form pentalaminar junctions by fusion of apposed trilaminar double leaflet membranes. These junctions appear to be candidates for low resistance pathways between muscle fibers. The muscles depolarize slowly when bathed in solutions containing elevated concentrations of KCl, and the sucrose gap method can then be used to measure the potential difference between polarized and depolarized regions. Thus the junctions which we have observed may provide the structural basis for electrical transmission through the sucrose gap.

Animals↗
PubMed1982

Studies on high affinity binding of mineralo- and glucocorticoids in rabbit aorta cytosol.

High affinity, specific binding-sites to mineralocorticoids and glucocorticoids, with characteristics of steroid receptors, have been found in rabbit aorta cytosol. Binding parameters (dissociation constants and number of binding sites per mg of cytosol protein) were determined from Scatchard plots, after statistical treatment of the data with the aid of a computer program, for the following tritiated steroids: 11-desoxycorticosterone (DOC), aldosterone (Aldo), progesterone (Prog), corticosterone (BK), cortisol (FK) and dexamethasone (Dex). The specificity of binding was then examined by means of steroid competition studies. The results of these experiments indicate that three different types of high-affinity binding sites to adrenal steroids are present in aorta cytosol: Type A, with the highest affinity for DOC; Type B, with the highest affinity for FK; Type C, with the highest affinity for Dex. In accordance with the relative competitive potencies of various steroids for these binding sites, Type A is designated as the "arterial mineralocorticoid binder", clearly differing in its binding characteristics from the cytoplasmic mineralocorticoid binders in known target tissues to these steroids (e.g. the renal receptor), while Type C is designated as the "arterial glucocorticoid binder", closely resembling the classical glucocorticoid receptor in known target tissues to glucocorticoids. Type B exhibited some of the binding characteristics of transcortin and may represent a modified, intracellular transcortin. While Types B and C are present also in the cytosol of inferior vena cava. Type A was only in the aorta. The role of these binders is not known at present. Arguments are presented in favor of a hypothesis that the Type A (mineralocorticoid) binder represents an arterial wall; and that, under certain conditions, this action leads to an increased contractility of arterial and arteriolar smooth muscles, increased peripheral resistance and hypertension.

Animals↗
PubMed1982

Adenovirus type 12 transformation involves loss of beta-adrenergic receptors and isoproterenol responsiveness.

The responsiveness of a growth-regulated rat 3Y1 cell line and five clones of 3Y1 cells transformed by the highly oncogenic human adenovirus type 12 to the catecholamine hormone (-)-isoproterenol was studied. The untransformed cells contained beta-adrenergic receptors characterized by specific binding of the beta-adrenergic receptor antagonist (-)-[3H]dihydroalprenolol, a 9- to 12-fold increase in cyclic AMP production in intact cells after incubation with 10 microM (-)-isoproterenol, and significantly increased adenylate cyclase (ATP pyrophosphatelyase [cyclizing], EC 4.6.1.1) activity in the presence of the hormone. In contrast, (-)-isoproterenol (10 to 100 microM) had no apparent effect on cyclic AMP production or the basal adenylate cyclase activity in the transformed cell lines. Binding studies revealed that untransformed cells contained approximately 19,400 beta-adrenergic receptor sites per cell. Three transformed cell clones tested showed a three- to fourfold loss of beta-adrenergic receptors.

Adenoviruses, Human↗