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γ‐Glutamylcyclotransferase in tobacco suspension cultures: Catalytic properties and subcellular localization
Author(s) -
Steinkamp Reinhard,
Schweihofen Barbara,
Rennenberg Heinz
Publication year - 1987
Publication title -
physiologia plantarum
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.351
H-Index - 146
eISSN - 1399-3054
pISSN - 0031-9317
DOI - 10.1111/j.1399-3054.1987.tb09231.x
Subject(s) - methionine , nicotiana tabacum , enzyme , substrate (aquarium) , cysteine , biochemistry , chemistry , enzyme assay , subcellular localization , ammonium sulfate , ammonium , cytoplasm , biology , chromatography , amino acid , organic chemistry , ecology , gene
Steinkamp, R., Schweihofen, B. and Rennenberg, H. 1987. γ‐Glutamylcyclotransfer‐ase in tobacco suspension cultures: Catalytic properties and subcellular localization. γ‐Glutamylcyclotransferase activity (EC 2.3.2.4) in ammonium sulfate precipitates (40–70% saturation) of extracts from cultured tobacco cells ( Nicoliana tabacum L. cv. Samsun) was analyzed as liberation of 5‐oxo‐proline from L‐γ‐glutamyl dipeptides. The enzyme was highly specific for the sulfur containing γ‐glutamyl dipeptides γ‐glutamyl‐L‐methionine and γ‐glutamyl‐i.‐cysteine. Maximum activity was obtained at pH 8.7 and 35°C. As also observed with animal γ‐glutamylcyclotransferase, the tobacco enzyme exhibited a relatively low substrate affinity (γ‐glutamyl‐i.‐methionine: K m 2.2 ± 0.4 mM ). In contrast to animal γ‐glutamylcyclotransferase, the tobacco enzyme was not inhibited by the D‐isomerof the substrate D‐γ‐glutamyl‐i.‐methionine; it also did not use the D isomer as a substrate. γ‐Glutamylcyclotransferase of tobacco cells was shown to be a soluble enzyme entirely localized in the cytoplasm.