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Biomedical subjects

D C Lin

Publications and source records attributed to D C Lin.

At least 55 records · Page 3Linked to original sources
PubMed1985

beta-Hydroxydecanoylthioester dehydrase: a rapid, convenient, and accurate product distribution assay.

High-performance liquid chromatography on silica gel has been used to separate the products from incubation of substrates with beta-hydroxydecanoylthioester dehydrase (Escherichia coli). Peaks are detected by their absorbances at 230 nm. Following correction for differences in extinction coefficients, comparison of the peak areas reveals the relative amounts of beta-hydroxydecanoate, E-2-decenoate, and Z-3-decenoate thioesters of N-acetylcysteamine.

Chromatography, High Pressure Liquid↗
PubMed1984

On the mechanism for inactivation of cytochalasin binding activity associated with F-actin and spectrin-band 4.1-actin complex by sulfhydryl reagents.

The sulfhydryl group modifying reagent, p-hydroxymercuribenzoate, inhibited the cytochalasin binding activity of the actin nuclei in the spectrin-band 4.1-actin complex from the erythrocyte membrane and of muscle F-actin. Kinetic studies indicated that while the cytochalasin binding activity was immediately inhibited, the actin remained filamentous and depolymerized slowly over a period of 1 to 2 h. Scatchard analysis of the binding data revealed that initially only the KD was affected. However, prolonged incubation led to depolymerization of the F-actin and dissociation of the spectrin-band 4.1-actin complex, resulting in loss of binding sites. It thus appears that certain actin sulfhydryl group(s) are important for cytochalasin binding. However, the most reactive sulfhydryl group (cys-374) on actin does not appear to be involved.

Actins↗
PubMed1983

Complexes containing actin and spectrin from erythrocyte and brain.

A complex of proteins with properties similar to those of erythrocyte spectrin-band 4.1-actin complex has been identified in a preparation derived from bovine brain. The complex has an apparent sedimentation coefficient of about 26S, and contains brain spectrin (also called fodrin) and actin as major components. The actin in the complex is in the oligomeric form, which nucleates assembly of actin filaments that grow from the "barbed" end. The complex cross-links actin filaments, resulting in an increase in low-shear viscosity. Whether the complex contains a protein analogous to erythrocyte band 4.1 is not known. However, it can be demonstrated that brain spectrin has the capability to interact with band 4.1 in a way which increases its ability to cross-link actin filaments.

Actins↗
PubMed1982

The capactins, a class of proteins that cap the ends of actin filaments.

A number of proteins that bind specifically to the barbed ends of actin filaments in a cytochalasin-like manner have been purified to various degrees from a variety of muscle and non-muscle cells and tissues. Preliminary evidence also indicates that proteins that interact with the pointed ends of filaments are present in skeletal muscle. Because of their ability to cap one or the other end of an actin filament, we have designated this class of proteins as the 'capactins'. On the basis of their effect on actin filament assembly and interaction in vitro, we propose that the capactins play important roles in cellular regulation of actin-based cytoskeletal and contractile functions. Our finding that the disappearance of actin filament bundles in virally transformed fibroblasts can be correlated with an increase in capactin activity in the extracts of these cells is consistent with this hypothesis.

Actins↗
PubMed1981

Spectrin-4.1-actin complex of the human erythrocyte: molecular basis of its ability to bind cytochalasins with high-affinity and to accelerate actin polymerization in vitro.

The spectrin-4.1-actin complex isolated from the cytoskeleton of human erythrocyte was found to be similar to muscle F-actin in several aspects: Both the complex and F-actin nucleate cytochalasin-sensitive actin polymerization; both bind dihydrocytochalasin B with similar binding contrasts; both can be depolymerized by DNase I with loss of cytochalasin binding activity. From these results, we conclude that the actin in the complex is in an oligomeric form. However, the presence of spectrin and band 4.1 in the complex not only stabilized the actin in the complex as evidenced by its resistance to depolymerization in low-ionic-strength conditions and to DNase I as compared with F-actin, but also altered the characteristics of the binding site(s) for cytochalasins believed to be located at the "barbed" (polymerizing) end of the oligomeric actin.

Actins↗
PubMed1980

Cytochalasins inhibit nuclei-induced actin polymerization by blocking filament elongation.

Polylysine was found to induce polymerization of muscle actin in a low ionic strength buffer containing 0.4 mM MgCl2. The rate of induced polymerization was dependent on the amount and on the molecular size of the polylysine added. A similar effect was obtained by adding actin nuclei (containing about 2-4 actin subunits) cross-linked by p-N,N'-phenylenebismaleimide to G-actin under the same conditions, suggesting that the effect of polylysine is due to promotion of the formation of actin nuclei. Polymerization induced by polylysine and by cross-linked actin nuclei was inhibited by low concentrations (10(-8)-10(-6)M) of cytochalasins. Binding experiments showed that actin filaments, but not actin monomers, contained high-affinity binding sites for [3H]cytochalasin B (one site per 600 actin monomers). The relative affinity of several cytochalasins for these sites (determined by competitive displacement of [3H]dihydrocytochalasin B) was: cytochalasin D greater than cytochalasin E approximately equal to dihydrocytochalasin B. The results of this study suggest that cytochalasins inhibit nuclei-induced actin polymerization by binding to highly specific sites at the point of monomer addition, i.e., the elongation site, in actin nuclei and filaments.

Actins↗
PubMed1980

Spin-label studies of erythrocytes in myotonic dystrophy: no increase in membrane fluidity.

The basic defect in myotonic dystrophy is thought to involve muscle cell membranes. Butterfield and associates have recently presented electron spin resonance data that suggest increased fluidity of erythrocyte membranes in patients with myotonic dystrophy. We studied erythrocytes from 11 patients with myotonic dystrophy and 14 age-matched controls, using spin-labeled fatty acid and ester probes. Despite attempts to reproduce the previously reported experimental conditions exactly, we found no significant differences in the electron spin resonance spectra of erythrocytes from normal and myotonic dystrophy subjects. These findings do not provide evidence of increased erythrocyte membrane fluidity in myotonic dystrophy; they fail to support the concept of an intrinsic defect of the lipid membrane in this disorder.

Adult↗
PubMed1979

Meperidine and normeperidine levels following meperidine administration during labor. I. Mother.

Because of the unavailability of sensitive analytic techniques, the pharmacokinetics of meperidine have not been clearly delineated in obstetric patients during labor. Moreover, the production of the active meperidine metabolite--normeperidine--has not been investigated. By means of gas chromatographic and mass spectrometric techniques, these characteristics of meperidine metabolism were evaluated in 23 pregnant patients in the present study. The data show that the disappearance curve and pharmacokinetic constants for meperidine are similar to those previously reported for nonpregnant subjects. In regard to normeperidine, the data indicate that it is produced within ten minutes after meperidine injection, increases rapidly for the next 20 minutes, and then slowly increases throughout labor. The results enumerate the pharmacokinetic constants of meperidine in obstetric patients and describe the appearance of normeperidine, the active meperidine metabolite, following meperidine administration during labor.

Adult↗
PubMed1979

Meperidine and normeperidine levels following meperidine administration during labor. II. Fetus and neonate.

The time interval between the administration of meperidine to laboring patients and delivery may affect neonatal status, but sophisticated analytic techniques have not been used to determine the exposure of the fetus to meperidine at various drug-delivery intervals. By means of gas chromatography and mass spectrometry, the concentrations of meperidine and normeperidine (the principle metabolite of meperidine) were quantitated in the umbilical cord venous and arterial plasma at delivery and in the urine of the neonate for three days postpartum. Following 50 mg. of meperidine administered intravenously during labor, fetal exposure to meperidine was highest two to three hours after maternal medication while fetal exposure to normeperidine was highest four hours or more after medication. We conclude from this study that there is a definite but nonlinear relationship between the drug-delivery interval and the amount of meperidine and normeperidine an infant receives; and that the drug-delivery intervals resulting in maximum fetal exposure reported here correspond with those resulting in maximum neonatal depression reported by others.

Chromatography, Gas↗
PubMed1979

Actin polymerization induced by a motility-related high-affinity cytochalasin binding complex from human erythrocyte membrane.

A high molecular weight complex (sedimentation coefficient approximately 27 S) containing high-affinity binding site(s) for [(3)H]dihydrocytochalasin B has been isolated from a low ionic strength extract of human erythrocyte membranes by sucrose density gradient centrifugation. Sodium dodecyl sulfate/polyacrylamide gel electrophoresis showed that actin, spectrin, and other minor components, including two polypeptides with the electrophoretic mobility of band 4.1, were present in the complex-containing fraction. Addition of this complex to a solution of muscle monomeric actin (G-actin) in a low ionic strength medium resulted in a rapid increase in viscosity to a level comparable to that of a solution of filamentous actin (F-actin). Electron microscopy showed that the viscosity increase reflected actin filament formation. The rate of induced actin polymerization was dependent on the amount of complex added to the G-actin; in less than 1 hr, less than 1 mug of protein from the complex-containing fraction induced the conversion of 0.4 mg of G-actin to the "F" from. Binding studies indicated that, upon polymerization of the actin, the cytochalasin binding complex became associated with the actin filaments. Low concentrations of cytochalasins D and E and dihydrocytochalasin B inhibited actin polymerization induced by the complex; the relative potencies of the drugs in inhibiting this process corresponded to their relative affinities for the complex, as well as their relative potencies in affecting cell motility. These results suggest that the cytochalasin binding complex functions as a regulatory site for cell motility by controlling formation and membrane attachment of actin-containing microfilaments in the cell.

Actins↗
PubMed1978

Specificity of the effects of cytochalasin B on transport and motile processes.

The effects of cytochalasin B (CB) and dihydrocytochalasin B (H2CB) on a variety of transport and motile processes have been compared. CB inhibited transport of D-glucose and L-glucose but not transport of thymidine in human erythrocytes. In contrast, H2CB, which differs from CB by the absence of a single double bond, had little or no effect on any of these processes. Both cytochalasins, however, affected the morphology of cultured fibroblasts and inhibited motile processes such as membrane ruffling, axon growth cone activity, blood clot retraction, cytoplasmic streaming, photodinesis, and cytokinesis. Determination of the partition coefficient of the two cytochalasins in several organic solvent/phosphate-buffered saline systems showed that H2CB has a higher affinity for the hydrophobic phase than CB. These results indicate that the inhibitory effects of CB on sugar transport and on cell motility and morphology are separable and independent events, mediated by the binding of the drug to specific cellular receptors.

Axons↗