Search results for "glutamine synthetase"

Transport-related amino acid metabolism in germinating barley grains

1987

When eight [14C]-labelled amino acids were separately injected into the endosperm of germinating (4 days at 20°C) barley (Hordeum vulgare L. cv. Himalaya) grains, the label was rapidly taken up by the scutellum and further transported to the shoot and roots. Some of the amino acids (leucine, lysine and asparagine) were transported in an intact form through the scutellum to the seedling, whilst glutamic acid and aspartic acid were largely converted to glutamine in the scutellum. Proline was mainly transported unchanged, but a small part of the label appeared in glutamine. Arginine was mostly broken down in the scutellum, possibly providing ammonia for the synthesis of glutamine. During furth…

Chloroplastic glutamine synthetase from Brassica napus.

1993

Glutamine synthetase from roots of Brassica napus. Nucleotide sequence of a cytosolic isoform.

1994

Purification and Characterization of Glutamine Synthetase Isoenzymes from Leaves and Roots of Brassica napus (L.)

1995

Summary The glutamine synthetase enzymes from leaves (GS2) and roots (GSR) of Brassica napus L. have been purified to homogeneity by the application of a three-stage isolation procedure comprising anion-exchange chromatography, adsorption by hydroxylapatite and gel filtration on Sephacryl 5-300 HR. The isoforms of the enzyme show a differential distribution in leaf and root tissues. Elution profiles of hydroxylapatite chromatography showed a distinct behaviour for GS proteins found in leaves and roots. Denaturing SDS-PAGE and Western blot experiments revealed molecular masses of approximately 43.5 and 40.5 kD for GS2 and GSR subunits, respectively. Moreover, kinetic properties determined us…

Studies on the Mechanism of Inhibition by Phosphinothricin of Glutamine Synthetase Isolated from Triticum aestivum L.

1986

Summary The activity of glutamine synthetase (EC 6.3.1.2) isolated from roots and leaves of wheat is strongly inhibited by phosphinothricin. As revealed by gel filtration and kinetic studies the mechanism of inhibition appears to be irreversible. The results indicate that the rate limiting step of the reaction of the inhibitor with the chloroplast glutamine synthetase is not the initial, but the following reaction. However, of root glutamine synthetase the irreversible inhibition follows a second order reaction depending on the concentration of the enzyme and of phosphinothricin and the rate limiting step is the formation of the initial enzyme-inhibitor complex. According to the kinetic dat…

The Effect of Phosphinothricin (Glufosinate) on Glutathione Synthesis in Plants

1990

The inhibitory effect of DL-phosphinothricin (glufosinate) on glutathione synthesis was studied in vivo and in vitro. The influence of phosphinothricin on γ-glutamylcysteine synthetase was compared with the already known effects of l-buthionine sulfoximine and l-methionine sulfoximine. The results showed that phosphinothricin and buthionine sulfoximine are inhibitors of γ-glutamylcysteine synthetase of plants. With both substances the enzyme was inhibited by 50 % at a concentration of 7 . 10−4M (pI50 = 3.15). Methionine sulfoximine reduced the enzyme activity by 50% at 5 . 10−2 M (pI50 = 1.30). It is discussed that the target enzyme of phosphinothricin is the glutamine synthetase whereas th…

Effect of Glufosinate (Phosphinothricin) and Inhibitors of Photorespiration on Photosynthesis and Ribulose-1,5-Bisphosphate Carboxylase Activity

1992

Summary Glufosinate (phosphinothricin) irreversibly inhibits glutamine synthetase and leads to a great decrease in the amino acids glutamine, glutamate, aspartate, serine, glycine and alanine. Due to the lack of glutamate and serine, the transamination of glyoxylate into glycine in the course of photorespiration cannot take place. The inhibition of this part of the photorespiratory process plays the essential role with respect to the photosynthesis inhibition caused by PPT under atmospheric conditions. After addition of different photorespiration or Calvin cycle intermediates to phosphinothricin no decrease in photosynthesis inhibition can be measured. This suggests that photosynthesis inhi…