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Biomedical subjects

C Kent

Publications and source records attributed to C Kent.

At least 235 records · Page 13Linked to original sources
PubMed1977

Lipid and polypeptide components of the crystalline yolk system from Xenopus laevis.

The polypeptide and lipid components of the crystallinelipoprotein-phosphoprotein from the yolk system of Xenopus laevis are described. This lipoprotein complex contains 17% lipid of which 75% is phospholipid. The phospholipid fraction consists of mostly phosphatidylcholine and phosphatidylethanolamine. The neutral lipid fraction contains mainly triglyceride. The phosphoprotein, phosvitin, has been separated from the lipoprotein, lipovitellin, by classical methods. Three polypeptide chains can be observed in the lipoprotein and their molecular weights as determined by sodium dodecyl sulfate gel electrophoresis are 105,500, 35,500, and 32,000. Phosvitin behaves abnormally on these gels, but analysis of the results suggests Mr = approximately 16,000 to 19,000/polypeptide chain. The lipovitellin component of the yolk complex contains approximately 100 bound lipid molecules/dimer. The stoichiometry of the components of this crystalline lipoprotein system is discussed in terms of the results obtained in this study and those of other workers.

Amino Acids↗
PubMed1976

Phosphatidic acid phosphatase and phospholipdase A activities in plasma membranes from fusing muscle cells.

Plasma membrane from fusing embryonic muscle cells were assayed for phospholipase A activity to determine if this enzyme plays a role in cell fusion. The membranes were assayed under a variety of conditions with phosphatidylcholine as the substrate and no phospholipase A activity was found. The plasma membranes did contain a phosphatidic acid phosphatase which was optimally active in the presence of Triton X-100 and glycerol. The enzyme activity was constant from pH 5.2 to 7.0, and did not require divalent cations. Over 97% of the phosphatidic acid phosphatase activity was in the particulate fraction. The subcellular distribution of the phosphatidic acid phosphatase was the same as the distributions of the plasma membrane markers, (Na+ + k+)-ATPase and the acetylcholine receptor, which indicates that this phosphatase is located exclusively in the plasma membranes. There was no detectable difference in the phosphatidic acid phosphatase activities of plasma membranes from fusing and non-fusing cells.

Adenosine Triphosphatases↗
PubMed1976

Observations on the localization of recently synthesized catecholamines in chromaffin cells after the injection of L-(2,5,6-3H)dopa.

The fate of tl-[2, 5, 6-3h] dopa, and the intracellular localization of its metabolic products dopamine, noradrenaline and adrenaline, have been determined by the simultaneous use of assay techniques following separation of amines by chromatography and light and electron microscopic autoradiography. During the first 24 h after i.v. or i.p. injection of [3H] DOPA, synthesis of the above catecholamines occurred. Throughout this time the labelled amines were associated with chromaffin granules or immediately adjacent cytosol and not with either the Golgi complex or rough endoplasmic reticulum. Labelling of chromaffin granules occurred simultaneously throughout the cell and there was no evidence of regions containing recently labelled granules and others containing previously charged (older) granules. Adrenaline-storing cells took up [3H] DOPA and its products more rapidly and lost recently synthesized adrenaline more rapidly than noradrenaline-storing cells took up and stored their equivalent amines. This was in keeping with a more rapid turnover of catecholamines in adrenaline-storing elements.

Adrenal Glands↗
PubMed1974

The nature of hypthalamo-neurohypophyseal neurosecretion in the rat. A study by light- and electron microscope autoradiography.

The nature of hypothalamo-neurohypophyseal neurosecretion was examined in the rat by means of intraventricular injections of tritiated amino acids. Quantitation of autoradiographs was used at the light microscope level to study the sites of synthesis of proteins and their time of arrival in the neural lobe. Electron microscope autoradiographs were used to study the labeling of neural lobe tissue. It was concluded that the great majority of the labeled material was translocated inside dense-cored granules and was probably composed mostly of neurophysins. The effect of ether anesthesia was also examined. It was found to remove the dense cores from about 20% of the granules in the neural lobe tissue, a process accompanied by the loss of most of their labeled material. The mechanism of the ether effect is discussed and compared to the normal secretion process.

Animals↗
PubMed1973

Plasma membranes from cultured muscle cells: isolation procedure and separation of putative plasma-membrane marker enzymes.

Partially purified plasma membranes were obtained from chick-embryo muscle cells grown in tissue culture. The purification procedure involved homogenization in buffered isotonic sucrose followed by differential and sucrose density gradient centrifugations. The activities of five plasma-membrane markers, as well as microsomal and mitochondrial markers, were followed throughout the purification. When cultures were labeled with [(125)I]alpha-bungarotoxin, which binds to the surface of cultured muscle cells, the distributions of bound alpha-bungarotoxin and Na(+),K(+)-ATPase (EC 3.6.1.3) activity were nearly identical. The activities of these two plasma-membrane markers were maximal in the upper two fractions of the sucrose density gradient and were purified 5- to 7-fold with respect to total particulate protein. These fractions contained 20-30% of the Na(+),K(+)-ATPase activity and bound alpha-bungarotoxin, 4% of the microsomal marker TPNH-dependent cytochrome c reductase, 0.2% of the mitochondrial marker succinate-dependent cytochrome c reductase, 2.7% of the cellular RNA, and 0.02% of the DNA. The activity of the commonly used plasma-membrane marker, 5'-nucleotidase (EC 3.1.3.5), was low in the upper two sucrose gradient fractions and was maximal in a more dense fraction. The distributions of the other two plasma-membrane markers, leucyl beta-naphthylamidase and phosphodiesterase I, were intermediate between Na(+),K(+)-ATPase and 5'-nucleotidase. The distributions of all markers were similar in preparations from cultures containing mononucleated myogenic cells, multinucleated myotubes, fibroblasts, or all three cell types. Modification of the procedure to include homogenization in the absence of sucrose resulted in a 3.4-fold purification of the membranes containing 5'-nucleotidase, which were shifted to a lower density.

Adenosine Triphosphatases↗
PubMed1973

Procedure for the isolation of mutants of Bacillus subtilis with defective cytoplasmic membranes.

A procedure has been devised to isolate mutants of Bacillus subtilis with structurally defective membranes. The procedure used to screen for the mutants involved comparison of the stability of protoplasts of the mutant with those of the wild type in a medium of sufficient osmotic strength to stabilize wild-type protoplasts. Mutagenized cells were grown as clones on agar plates, and then replicated onto plates containing 0.5 m lactose, which is sufficient to stabilize wild-type protoplasts. The colonies on the lactose-containing plates were then treated with lysozyme to convert the cells to protoplasts. Colonies of wild-type protoplasts remained opaque; however, colonies of mutant protoplasts lysed and became clear. Twenty-nine osmotically fragile mutants were isolated in this manner; the membranes of several mutants were found to contain alterations in the composition of their proteins or lipids.

Bacillus subtilis↗
PubMed1972

An osmotically fragile mutant of Bacillus subtilis with an active membrane-associated phospholipase A 1 .

By use of a newly developed procedure for the isolation of mutants with osmotically fragile protoplasts, a mutant of Bacillus subtilis was isolated that has a very active enzyme system for the catabolism of phospholipids via the sequential action of a phospholipase A(1) (EC 3.1.1.4) and a lysophospholipase (EC 3.1.1.5). The wild-type bacteria contain no detectable phospholipase A(1) activity, but do contain a protein that specifically inhibits the phospholipase A(1) in the mutant. This protein may play an important role in the control of phospholipid catabolism.

Animals↗
PubMedDate not supplied

Septo-hippocampal cholinergic and neurotrophin markers in age-induced cognitive decline.

Messenger RNA (mRNA) molecules encoding proteins related to the presynaptic cholinergic and neurotrophin systems were quantitated in the hippocampus and basal forebrain of Long-Evans rats with spatial learning ability assessed in the Morris water maze. The reverse transcriptase-polymerase chain reaction showed that the mRNAs for the low-affinity neurotrophin receptor (p75-NTR) and the growth-associated protein GAP-43 were decreased in level in the basal forebrain of aged-impaired rats. In the hippocampus of these aged-impaired rats, the mRNA for VGF, another neurotrophin-inducible gene, also was decreased. In situ hybridization histochemistry revealed that mRNAs for nerve growth factor (NGF) and brain-derived neurotrophic factor increased in level in the aged rat hippocampus; when age effects were removed, NGF mRNA level remained significantly correlated with maze performance. Enzyme-linked immunosorbent assay indicated that NGF protein was expressed at normal levels in the aged rat hippocampus. These mRNA and protein alterations may signify that a defect in neurotrophin signaling exists in the brains of aged Long-Evans rats, underlying reduced plasticity responses in the basal forebrain cholinergic system.

Aging↗