Ammonia assimilation in <i>Vitis vinifera</i> L.: <p>II. Leaf and root glutamine synthetase</i>
DOI:
https://doi.org/10.5073/vitis.1983.22.299-305Abstract
Glutamine synthetase (GS) activity in Vitis vinifera L. cv. Chenin blanc leaf and root tissues was present in the supernatant and particulate fractions. The percentage distribution of GS activity in leaf and root extracts were respectively 39.5 and 49.2 % in the 10,000 gpellet, 38.6 and 41.1 % in the 2.3,500 gpellet, and 21.9 and 9.7 % in the 23,500 g supernatant fractions. Leaf GS activity was always greater than root enzyme activity. Kinetic studies revealed no significant differences between leaf and root GS from the 10,000 g pellet fraction. The Km values for L-glutamate, ATP and hydroxylamine were respectively 3.2 ± 0.7 mM, 0.8 ± 0.2 mM, and 0.8 ± 0.2 mM. Formation of y-glutamyl hydroxamate was linear for the first 35 min. Optimum in vitro reaction conditions were pH 7.70-8.10, incubation temperature 37 °C, and amount of enzyme equivalent to 75-105 mg of fresh tissue. L-arginine, L-ornithine and carbamyl phosphate at a concentration of 5 mM caused inhibition of 13.6 and 12 %, respectively.
Die Ammonium-Assimilation bei Vitis vinifera L.:
II. Die Glutaminsynthetase der Blätter und Wurzeln
Bei der Rebsorte Chenin blanc (Vitis vinifera L.) lag nach differenzierter Zentrifugation sowohl in den löslichen wie in den strukturierten Fraktionen Glutaminsynthetase-(GS-)Aktivität vor. Die prozentuale Verteilung der GS-Aktivität auf Blatt- und Wurzelextrakte betrug jeweils 39,5 und 49,2 % im 10 000-g-Sediment, 38,6 und 41,1 % im 23 500-g-Sediment sowie 21,9 und 9,7 % im 23 500-g-Überstand. In den Blättern war die GS-Aktivität stets höher als in den Wurzeln. Untersuchungen der Enzymkinetik erbrachten bei dem 10 000-g-Sediment keine signifikanten Unterschiede zwischen der GS-Aktivität der Blätter und der Wurzeln. Die Km-Werte für L-Glutamat, ATP und Hydroxylamin betrugen 3,2 ± 0,7 mM, 0,8 ± 0,2 mM und 0,8 ± 0,2 mM. Die Bildung von y-Glutamylhydroxamat verlief in den ersten 35 min linear. In vitro waren die optimalen Reaktionsbedingungen ein pH von 7,70-8,10, eine Inkubationstemperatur von 37 °C und eine Enzymmenge, die dem Gehalt von 75-105 mg Frischgewebe entsprach. L-Arginin, L-Ornithin und Carbamylphosphat in Konzentrationen von 5 mM hemmten die Enzymwirkung ·um 13,6 bzw. 12%.
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