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Biomedical subjects

L A Stocken

Publications and source records attributed to L A Stocken.

At least 37 records · Page 2Linked to original sources
PubMed1977

Phosphorylation of rat thymus histones, its control and the effects thereon of gamma-irradiation.

The phosphate content of rat thymus histones was determined. As expected for a replicating tissue, histones 1 and 2B were more phosphorylated and had higher 32P uptakes than did histones from resting liver nuclei; the other histones all showed 32P uptake, but the phosphate content and uptake of histone 2A was about half that for liver histone 2A. When thymus nuclei were incubated in a slightly hypo-osmotic medium, non-histone proteins and phosphorylated histones were released into solution; this was enhanced if ATP was present in the medium. [gamma-32P]ATP was incorporated into non-histone proteins, including protein P1, and into the ADP-ribosylated form of histone 1; negligible 32P was incprporated into the other, bound, histones. Histones 1 and 2B added to the incubation medium were extensively, and histones 2A and 4 slightly, phosphorylated. Histones released by increasing the ionic strength of the medium were phosphorylated. Added lysozyme and cytochrome c were neither bound nor phosphorylated, but added non-histone protein P1 was phosphorylated, causing other histones to be released from the nuclei, especially histones 2A and 3. The released histones were phosphorylated. gamma-Irradiation decreased 32P uptake into the non-ADP-ribosylated histones 1 and 4; phosphorylation of histone 1 in vitro was unaffected. The importance of non-histone proteins, ATP availability and nuclear protein kinases to the control of histone phosphorylation in vivo is discussed.

Adenosine Triphosphate↗
PubMed1975

Chemical and metabolic properties of adenosine diphosphate ribose derivatives of nuclear proteins.

1. ADP-ribose is found in rat liver nuclei covalently bound to histone F1, to a non-histone protein, and to a small peptide. 2. A single unit of ADP-ribose, covalently bound to phosphoserine, was isolated from an enzymic hydrolysate of histone F1. ADP-ribose-bearing peptides were isolated from a tryptic digest of the histone. 3. It is proposed that the 1'-hydroxyl group of ADP-ribose is linked to the phosphate group of phosphoserine in histone F1. 4. The incorporation of 32P into ADP-ribose on histone F1 a parallels the DNA content through the cell cycle. An increased incorporation of the nucleotide into the other derivatives is observed during S phase. 5. It is suggested that the ADP-ribose derivative of histone F1 has a role in maintaining the G0 state and that one or both of the other derivatives is concerned with control of DNA synthesis.

Adenosine Diphosphate Sugars↗
PubMed1973

The characterization of a non-histone protein isolated from histone F1 preparations.

A non-histone protein was obtained by extraction of nuclei derived from rat liver or thymus or ascites-hepatoma cells with 5% (w/v) HClO(4). Separation from histone F1 was achieved by chromatography on DEAE-cellulose. The purified component P1 was characterized and the formation of complexes with histone F1 and polylysine was studied.

Amino Acids↗
PubMed1973

Uptake of orotate and thymidine by normal and regenerating rat livers.

1. At 1h after operation livers from partially hepatectomized rats showed a 60-100% increase in the capacity to concentrate (3)H radioactivity from orotate, thymidine or uridine with respect to the radioactivity in plasma. Uptake of [(3)H]cytidine into liver was unaffected, as was entry of any precursor studied into any tissue other than liver. 2. This increase in intracellular radioactivity was detectable 10min after operation with both orotate and thymidine. With orotate the augmentation had disappeared by 3 days, but with thymidine it was still evident 8 days after partial hepatectomy, when [(3)H]thymidine incorporation into DNA was no longer increased. Competition studies established that orotate was not entering the liver by the same mechanism as thymidine. 3. In the soluble fraction of the liver all the (3)H radioactivity from orotate was present as uridine nucleotides. Thymidine was not phosphorylated, and was believed to be catabolized.

Aging↗
PubMed1973

Thymidine metabolism in regenerating rat liver one to two hours after practical hepatectomy.

1. When [(3)H]thymidine was injected intravenously into rats in amounts up to 40mg/kg body wt. and the (3)H radioactivity in the livers measured at 30min, saturation kinetics for thymidine uptake were not found. If the animals were examined 3 min after intravenous injection, saturation could be attained in normal rats with 12mg of thymidine/kg and in partially hepatectomized rats with 4mg/kg. At concentrations of thymidine close to saturation, no differences were found in rate or amount of uptake/g of liver between normal and partially hepatectomized rats 1-2h after operation. 2. Perfusion techniques were used to compare thymidine uptakes in the two sets of rats at concentrations up to 40mum-thymidine. Uptakes with tracer amounts of thymidine after 30min were identical in vivo and in the perfusion studies and were twice as great in livers from partially hepatectomized rats with concentrations up to 40mum-thymidine. 3. At 1.5h after operation there was nearly twice as much beta-aminoisobutyrate present per g of liver from partially hepatectomized as compared with normal rats.

Aminoisobutyric Acids↗
PubMed1972

Uptake of amino acids and nucleic acid precursors by regenerating rat liver.

1. At 0.5-1.0h after partial hepatectomy the intracellular acid-soluble fraction of rat liver took up twice as much radioactivity from [(3)H]orotic acid, [(3)H]uridine and [(3)H]thymidine as did similar fractions from sham-operated animals. This increase in penetration was not prevented by adrenalectomy or actinomycin, both of which decreased precursor uptake into nuclear RNA at this time. The increase in entry was still shown by thymidine at 22h after operation, at the height of the S period. Adenine penetration was not increased 1h after partial hepatectomy. 2. Plasma concentrations of ornithine and possibly methionine, tyrosine and lysine were raised 1.5h after partial hepatectomy. [(3)H]Lysine entry into regenerating liver at this time was increased by 60%; [(3)H]valine uptake was unaffected. Intracellular amounts of tyrosine, phenylalanine and ornithine in the liver were also increased. 3. The relation of these events to the start of liver regeneration is discussed.

Adenine↗
PubMed1971

Histone kinase and cell division.

1. The activity of the soluble phosphokinase for histone F1 increases in regenerating rat liver during the first period of DNA synthesis after partial hepatectomy. The increase probably represents new enzyme synthesis. 2. A dose of 500rd of gamma-irradiation given early in G1 decreases the amount of histone F1 phosphokinase found 22h after partial hepatectomy by 60-70%. 3. The enzyme preparations also contained a histone F1 phosphatase; the presence together of the kinase and phosphatase caused a disproportion between net (31)P uptake and (32)P incorporation into histone F1. 4. All four subclasses of histone F1 could accept phosphate from ATP. 5. Crude enzyme preparations transferred more (31)P into histone F1 with an initially low phosphate content than into one with a high phosphate content; conversely, more (32)P was transferred into the latter.

Adenosine Triphosphate↗
PubMed1971

Histone phosphokinase activity in nuclear and cytoplasmic cell fractions from normal and regenerating rat livers.

1. Liver cell fractions were prepared by non-aqueous procedures and nuclei were also obtained in a hyperosmotic sucrose medium. Histone phosphokinase activity, assayed with histone F1 as substrate, was present in the soluble fraction of the cytoplasm and also bound on to the chromatin fraction of the nucleus. 2. The activity of the enzyme increased sixfold in nuclei from regenerating livers 22h after partial hepatectomy. 3. The enzyme bound in the nucleus was only marginally activated by 1mum-3':5'-cyclic AMP which stimulated the cytoplasmic soluble enzyme fourfold. 4. Nuclei prepared by the non-aqueous technique were also able to phosphorylate histones F2a and F3 and showed histone phosphatase activity with histone F1 phosphate as substrate.

Animals↗
PubMed1970

Changes in proportion of thiol to disulphide in acid-soluble nuclear proteins of Echinus during the first cell cycle.

1. DNA synthesis in Echinus esculentus eggs kept at 10 degrees C takes place just after fusion, 0.75-1.5h after fertilization, and at telophase at about 2.67-3.33h after fertilization. 2. An increase in the thiol/thiol+disulphide ratio in acid extracts from washed nuclear fractions of the eggs is found at fusion, at early stages of mitosis and at telophase. When DNA is being synthesized, the relative amount of thiol in the extracts increases. 3. There are at least five thiol-containing histones in the acid extract together with a diffusible thiol peptide containing methyl-lysine and 3-methylhistidine and a thiol-containing acidic protein.

Amino Acids↗
PubMed1970

Histone F1. Purification and phosphorus content.

1. Two minor protein fractions (B and C) were separated from histone F1 by chromatography on DEAE-cellulose. Fraction B was acidic. 2. Uptake of (32)P in vivo into histone F1 but not into fractions B and C was stimulated by partial hepatectomy. 3. It is suggested that partial hepatectomy causes an increase in the number of histone F1 molecules phosphorylated.

Animals↗