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Biomedical subjects

A Korner

Publications and source records attributed to A Korner.

At least 37 records · Page 2Linked to original sources
PubMed1970

Amino acid requirement for the growth-hormone stimulation of incorporation of precursors into protein and nucleic acids of liver slices.

1. Incorporation of [(14)C]leucine into protein in rat liver slices, incubated in vitro, increased as the concentration of unlabelled amino acids in the incubation medium was raised. A plateau of incorporation was reached when the amino acid concentration was 6 times that present in rat plasma. Labelling of RNA by [(3)H]orotic acid was not stimulated by increased amino acid concentration in the incubation medium. 2. When amino acids were absent from the medium, or present at the normal plasma concentrations, no effect of added growth hormone on labelling of protein or RNA by precursor was observed. 3. When amino acids were present in the medium at 6 times the normal plasma concentrations addition of growth hormone stimulated incorporation of the appropriate labelled precursor into protein of liver slices from normal rats by 31%, and into RNA by 22%. A significant effect was seen at a hormone concentration as low as 10ng/ml. 4. Under the same conditions addition of growth hormone also stimulated protein labelling in liver slices from hypophysectomized rats. Tissue from hypophysectomized rats previously treated with growth hormone did not respond to growth hormone in vitro. 5. No effect of the hormone on the rate or extent of uptake of radioactive precursors into acid-soluble pools was found. 6. Cycloheximide completely abolished the hormone-induced increment in labelling of both RNA and protein. 7. It was concluded that, in the presence of an abundant amino acid supply, growth hormone can stimulate the synthesis of protein in rat liver slices by a mechanism that is more sensitive to cycloheximide than is the basal protein synthesis. The stimulation of RNA labelling observed in the presence of growth hormone may be a secondary consequence of the hormonal effect on protein synthesis. 8. The mechanism of action of growth hormone on liver protein synthesis in vitro was concluded to be similar to its mechanism of action in vivo.

Amino Acids↗
PubMed1969

Influence of amino acid supply on ribosomes and protein synthesis of perfused rat liver.

1. The livers of rats were perfused in situ with medium containing mixtures of amino acids in multiples of their concentration in normal rat plasma. The incorporation of labelled amino acid into protein of the liver and of the perfusing medium increased with increasing amino acid concentration. During 60min. perfusions, labelling of liver protein reached a plateau, and labelling of medium protein was inhibited when the initial concentration of the amino acid mixture was more than ten times the normal plasma value. 2. Examination of polysome profiles derived from livers perfused without amino acids in the medium showed that the number of large aggregates was decreased and the number of small aggregates, particularly monomers and dimers, was increased with time of perfusion. The addition of amino acids to the perfusion medium reversed this polysome shift to an extent that was dependent on the initial concentration of amino acids. Polysome profiles derived from livers perfused for 60min. with ten times the normal plasma concentration of amino acids were essentially the same as the polysome profiles of normal non-perfused livers. 3. The ability of ribosome preparations from perfused livers to incorporate amino acids into protein in vitro decreased with increasing time of perfusion when no amino acids were added to the medium, but increased as the concentration of amino acids in the perfusion medium was increased. 4. The ability of cell sap from perfused livers to support protein synthesis in vitro was not influenced by the amino acid concentration of the perfusion medium. 5. Livers were perfused for 60min. with medium containing amino acid mixtures at ten times the normal plasma concentration but deficient in one amino acid. Maximal incorporation of labelled amino acid into liver protein, the stability of the polysome profile and the ability of ribosome preparations to incorporate amino acids into protein were found to depend on the presence of 11 amino acids: arginine, asparagine, isoleucine, leucine, lysine, methionine, phenylalanine, proline, threonine, tryptophan and valine. A mixture of these 11 amino acids, at ten times their normal plasma concentration, stimulated the incorporation of labelled amino acid into liver protein, stabilized the polysome profile and increased the ability of ribosome preparations to incorporate amino acids into protein to the same extent as the complete mixture. 6. It is concluded that the availability of certain amino acids plays an important role in the control of protein synthesis, possibly by stimulating the ability of ribosomes to become, and to remain, attached to messenger RNA.

Amino Acids↗