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Biomedical subjects

J E Varner

Publications and source records attributed to J E Varner.

At least 55 records · Page 3Linked to original sources
PubMed1981

Estimation of protein turnover in soybean leaves using magic angle double cross-polarization nitrogen 15 nuclear magnetic resonance.

Magic angle cross-polarization 15N nuclear magnetic resonance spectra of intact lyophilized soybean leaves have been obtained at 9.12 MHz. The leaves were harvested over a 6-week period from 15N-uniformly labeled plants exposed to 13CO2 for 1 to 7 days. The concentration of 13C-15N double labels in the main chains of leaf protein was determined nondestructively by double cross-polarization techniques. Both incorporation and turnover rates of these double labels were estimated and together lead to the conclusion that the protein of a mature, fully expanded soybean leaf is fairly long lived, with a half-life of about 30 days.

Kinetics↗
PubMed1981

Asparagine amide metabolism in developing cotyledons of soybean.

Magic-angle single and double cross-polarization (13)C and (15)N NMR spectra have been obtained of lyophilized soybean cotyledons cultured on media containing, as the only nitrogen source, [4-(13)C, amide-(15)N]asparagine. Single cross-polarization NMR shows directly and unambiguously that both labels from asparagine are incorporated extensively and nonrandomly into protein by the developing cotyledon during a 2-week period. A stable-isotope double label tags a chemical bond. The metabolic fate of the asparagine double label was followed by double cross-polarization NMR using the latter's sensitivity to the dipolar coupling between directly bonded (13)C and (15)N. These experiments show that in culture the direct incorporation of asparagine (with no scrambling of label) accounts for about half of all asparagine residues in soybean protein. This conclusion implies the operation of a regulatory apparatus in soybeans for both direct utilization and degradation of asparagine in protein synthesis.

Journal Article↗
PubMed1980

Purification and Characterization of a Salt-extractable Hydroxyproline-rich Glycoprotein from Aerated Carrot Discs.

The salt-extractable hydroxyproline-rich glycoprotein (HRGP) of the cell wall of aerated carrot root discs has been studied by polyacrylamide gel electrophoresis. The predominant proline-labeled protein extractable from the cell wall is rich in hydroxyproline as shown by its specific loss of (3)H from proline labeled in position 4 and its shift in electrophoretic mobility after labeling in the presence of an inhibitor of hydroxyproline synthesis. Unlabeled HRGP can be identified by staining gels for carbohydrate. The HRGP has been purified by ion exchange chromatography and CsCl gradient centrifugation. The HRGP consists of about 50% protein and 50% carbohydrate with an overall molecular weight of 86,000. The amino acid composition of the protein portion consists of 50% hydroxyproline, 19% basic amino acids, 12% serine, and 10% tyrosine. This glycoprotein accumulates in a salt-extractable pool in the cell wall beginning between 10 and 20 hours of aeration and may also become incorporated into the nonextractable portion of the cell wall.

Journal Article↗
PubMed1974

Hormonal control of messenger ribonucleic acid metabolism in barley aleurone layers.

Ribonucleic acid containing poly(adenylic acid) [poly(A)-RNA] is present in barley aleurone layers. This poly(A)-RNA becomes labeled with radioactive precursors of RNA during the incubation of isolated aleurone layers with or without gibberellic acid. However, the rate of synthesis of poly(A)-RNA is enhanced by gibberellic acid. This enhancement begins within 3-4 hr of addition of the hormone and reaches a maximum, which is about 50-60% over the control, 10-12 hr after addition of the hormone. Cordycepin inhibits total RNA as well as poly(A)-RNA synthesis in barley aleurone layers. However, cordycepin inhibits the hormone-controlled synthesis of alpha-amylase (EC 3.2.1.1) only if it is added 12 hr or less after gibberellic acid. The insensitivity of alpha-amylase production to cordycepin after 12 hr of gibberellic acid treatment suggests that alpha-amylase is translated from stable messenger RNA.

Adenine Nucleotides↗
PubMed1973

Control of the formation of amylases and proteases in the cotyledons of germinating peas.

Protease activity increased in attached cotyledons of germinated peas (Pisum sativum L. cv. Alaska) as the stored proteins declined but did not increase in excised cotyledons incubated for the same length of time. Cotyledons of seeds germinated in the presence of a casein hydrolysate solution developed less protease activity than did those germinated on water. These results suggest that accumulation of amino acids regulates the protease level in the cotyledons of germinating peas.In contrast to protease, alpha- and beta-amylase increased during incubation of excised pea cotyledons. Their increase was inhibited by abscisic acid. Abscisic acid did not inhibit (14)C-leucine incorporation into protein or reduce the respiratory rate in the cotyledons; hence, its effect on amylase formation was not the result of a general inhibition of metabolism. An ether-soluble acid fraction, which would contain any abscisic acid present in the material, inhibited amylase formation more when it was obtained from imbibed seeds than when it was obtained from cotyledons of seeds germinated for 10 days. These and other results suggest that amylase formation in germinating peas is regulated by abscisic acid.

Journal Article↗
PubMed1973

Hormonal control of orthophosphate incorporation into phospholipids of barley aleurone layers.

Gibberellic acid added to isolated barley aleurone layers enhances orthophosphate incorporation into chloroform-methanol-soluble compounds. The effect is measurable at 4 to 6 hours after the addition of gibberellic acid and reaches a maximum after 8 to 12 hours. The increase in the rate of orthophosphate incorporation is 3- to 5-fold over the rate in control layers incubated without gibberellic acid.The gibberellic acid enhancement of the rate of phospholipid labeling is inhibited within 1 to 2 hours by cycloheximide, 6-methylpurine, and abscisic acid.The increase in labeling of phospholipids occurs throughout the subcellular fractions rather than being restricted to a specific fraction or organelle. The increase in radioactivity in phospholipids as shown by thin layer chromatography is due to a proportional increase in all phospholipids.The enhancement by gibberellic acid of the rate of phospholipid labeling may be required for the subsequent production of gibberellic acid-induced hydrolases.

Journal Article↗
PubMed1972

Characteristics of the process of enzyme release from secretory plant cells.

Secretion-the outward movement of molecules across the plasmalemma-of alpha-amylase by barley (Hordeum vulgare L. cv. Himalaya) aleurone layers is an energy-dependent process that is not directly dependent upon protein synthesis or RNA synthesis and does not appear to be under the direct control of gibberellic acid or abscisic acid. Release-the movement of the secreted alpha-amylase molecules through the walls into the surrounding medium-is apparently diffusion limited and is markedly dependent upon the presence of ions.

Journal Article↗
PubMed1972

Hormonal control of polyribosome formation in barley aleurone layers.

The addition of abscisic acid to barley (Hordeum vulgare L. cv. Himalaya) aleurone layers at the same time as gibberellic acid completely prevents the gibberellin-induced increases in the percentage of polysomes, the formation of polyribosomes, and the synthesis of alpha-amylase, even when the molar concentration of gibberellic acid is four times greater than the concentration of abscisic acid. The addition of abscisic acid to aleurone cells producing alpha-amylase (midcourse addition) inhibits the further synthesis of alpha-amylase and decreases the percentage of polysomes but does not change the number of ribosomes per cell.The removal of gibberellic acid from aleurone layers during the midcourse of alpha-amylase production arrests alpha-amylase synthesis and decreases the percentage of polysomes. Readdition of gibberellic acid causes the reinitiation of the synthesis of alpha-amylase and a return of the percentage of polysomes to the original level.The incubation of aleurone layers with 5-fluorouracil inhibits the secretion of alpha-amylase. The changes in polysomes isolated from cells treated with either fluorouracil or actinomycin D correlate with the changes in enzyme synthesis caused by the addition of these inhibitors.Gibberellic acid and abscisic acid affect both the conversion of monosomes to polysomes and the synthesis of new ribosomes. The gibberellin-stimulated increases in the number of ribosomes and the percentage of polysomes are probably a prerequisite for the hormone induction of enzyme synthesis.

Journal Article↗