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1984
Journal Article
Titel
Gamma-glutamyl-transpeptidase in tobacco suspension cultures - Catalytic properties and subcellular localization
Abstract
Gamma-Glutamyl-transpeptidase activity (EC 2.3.2.2) was found in ammonium sulfate precipitates of extracs from cultured cells of Nicotiana tabacum L. var.Samsun. Specific activity up to 3.2 nmol (mg protein) E-1 min E-1 was achieved, using the artificial substrate gamma-glutamyl-p-nitroanilide (K sub m 0.6 mM) instead of glutathione. Optimal enzyme activity was obtained at pH 8.0-8.5 and 45 degrees C. The enzyme reaction was inhibited competitively by gamma-glutamyl analogs (6-diazo-5-oxo-L-norleucine: K sub i 0.76 myM; L-azaserine: K sub i 0.23 mM) or the inorganic ion m-periodate (K sub i 0.43 mM). Cell fractionation and in vivo experiments revealed that 77% of the gamma-glutamyl-transpeptidase activity is localized in the soluble cytoplasmic fraction, while 20-23% of the enzyme is found on the outer surface of the plasmalemma. (IFU)