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5‐Oxo‐prolinase in Nicotiana tabacum: catalytic properties and subcellular localization
Author(s) -
Rennenberg Heinz,
Stcitikamp Reinhard,
Kesselmeier Juergen
Publication year - 1981
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.1399-3054.1981.tb08496.x
Subject(s) - nicotiana tabacum , divalent , enzyme , substrate (aquarium) , proline , enzyme assay , chemistry , biochemistry , cytoplasm , purine , nucleotide , amino acid , biology , organic chemistry , ecology , gene
5‐Oxo‐prolinase of cultured tobacco cells is a soluble enzyme predominantly localized in the cytoplasm. To get optimal enzyme activity, the presence of the monovalent cation ammonium and the divalent cations Mg 2+ and Mn 2+ in the assay mixture is necessary. The enzyme has an extremely alkaline pH—(9.5–10.5) and a high temperature ‐ optimum (55°C). In contrary to the 5‐oxo‐prolinase from animal cells, where heat‐stabilization by 5‐oxo‐proline is observed, the high temperature optimum of the tobacco enzyme is due to stabilization by ATP. High 5‐oxo‐prolinase activity in tobacco cell homogenates was not only shown with the co‐substrate ATP, but with other purine‐nucleotides, too, although ATP was the best co‐substrate of the compounds tested. Substrate affinity of the tobacco enzyme (K m 5‐oxo‐proline = 30.5 μM) is similar to that demonstrated for wheat germ 5‐oxo‐prolinase. Competitive inhibition by the 5‐oxo‐proline analogues 2‐imidazolidone‐4‐carboxylic acid(K 1 = 14.5 μ M ) and dihydroorotic acid (K 1 =2 m M ) revealed a much higher sensitivity of tobacco 5‐oxo‐prolinase to these compounds than observed for the mammalian enzyme.