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Biomedical subjects

A Sen

Publications and source records attributed to A Sen.

At least 217 records · Page 12Linked to original sources
PubMed1981

The structure and thermotropic properties of pure 1,2-diacylgalactosylglycerols in aqueous systems.

Pure 3-sn-monogalactosyldilinolenoylglycerol and 3-sn-digalactosyldilinolenoylglycerol have been isolated from bean leaves. Distearoyl derivatives have been prepared by catalytic hydrogenation of the unsaturated galactolipids. The unsaturated lipids form stable monomolecular films at the air/water interface which are similar to liquid-expanded phospholipid monolayers. The limiting areas were about 0.57 nm2 and 0.62 nm2 for the mono- and digalactosyldiacylglycerols, respectively. The saturated galactolipids formed condensed monolayers that were relatively unstable. The surface pressure-area isotherm of the digalactosyl derivative was more expanded than that of the monogalactosyldiacylglycerol especially at low surface pressures. Low-angle X-ray diffraction and freeze-fracture electron microscopy studies of the monogalactosyldiacylglycerols showed that an hexagonal-type structure was formed by the unsaturated lipid in aqueous systems, whilst the saturated lipid was arranged in a lamellar configuration. Both digalactosyldiacylglycerols form lamellar structures in water. A gel-to-liquid-crystalline phase transition of distearoyldigalactosylglycerol was observed at about 51 degrees C by fluorescence depolarization measurements, using 1,6-diphenylhexatriene, and by differential scanning calorimetry. The saturated monogalactosyldiacylglycerol did not form dispersions suitable for fluorescence probe studies of a phase transition. A complex pattern of endotherms was observed for this lipid by differential scanning calorimetry.

Chemical Phenomena↗
PubMed1981

Purified low-molecular-weight protein kinase from murine sarcoma virus particles catalyzes tyrosine phosphorylation endogenously but phosphorylates cellular proteins at serine.

The low-molecular-weight (LMW) protein kinase associated with high-titer murine sarcoma virions have been extensively purified by ammonium sulfate fractionation. Bio-Gel P-100 gel filtration, DEAE-cellulose and carboxymethyl cellulose chromatography. The purified enzyme migrates as a 16K polypeptide in polyacrylamide gel electrophoresis in the presence of sodium dodecyl sulfate. The enzyme catalyzes phosphotransfer with ATP as a phosphate donor to various exogenously added proteins as acceptors; it requires Mg2+ and is independent of cyclic AMP. The enzyme preparation catalyzes a low level of phosphorylation in the absence of any exogenously added substrate and forms phosphotyrosine. However, in the presence of acceptor protein molecules including total soluble cytoplasmic proteins of murine sarcoma virus-transformed mouse cells, the phosphorylated end products contain predominantly phosphoserine. The virion-associated enzyme also shows a preference for phosphorylating certain polypeptides in the soluble cytoplasmic extracts of murine sarcoma virus-transformed cells.

Adenosine Triphosphate↗
PubMed1980

The crystal structure of tortoise egg-white lysozyme at 6 A resolution.

Lysozyme extracted from the egg-white of tortoise, the first example of a reptilian lysozyme to have been purified, has been crystallized and its tertiary structure determined at low resolution by X-ray analysis. This structure is shown to be closely homologous to that of hen egg-white lysozyme. The crystals of tortoise egg-white lysozyme contain a large proportion of liquid and the X-ray map shows that this forms large channels through the crystals into which the active sites of the enzyme molecules open. This indicates that tortois lysozyme crystals may be suitable for low-temperature studies of true enzyme substrate complexes.

Animals↗
PubMed1980

Direct association of fibronectin and actin molecules in vitro.

Affinity chromatography with actin-Sepharose conjugates of purified human fibronectin, normal human plasma, or serum-free culture fluid from human fibroblasts showed that fibronectin molecules can directly bind to actin. A quantitative recovery of soluble human fibronectin was accomplished by chromatography on actin immobilized on Sepharose beads. Human fibronectin molecules bound to actin-Sepharose were eluted with 0.25--0.35 M potassium bromide, and these molecules competed in a species-specific radioimmunoassay for human fibronectin. The subunits of fibronectin isolated by actin-Sepharose chromatography comigrated in SDS polyacrylamide gel electrophoresis with those of electrophoretically homogeneous fibronectin purified by conventional procedures. The efficient direct binding of fibronectin to actin suggests that interactions between these proteins might also take place in vivo but further studies are needed to elucidate the biological significance of this affinity.

Actins↗