5-Oxo-prolinase in Nicotiana tabacum: catalytic properties and subcellular localization [glutathione, tobacco, tissue culture]
1981
Rennenberg, H. | Steinkamp, R. | Kesselmeier, J. (Koeln Univ. (Germany, F.R.). Botanisches Inst.)
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 deg C). In contrast to the 5-oxo-prolinase from animal cells, where heat-stabliization 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 mu-M) 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(, I) = 14.5 mu-M) and dihydroorotic acid (K(, I) = 2mu-M) revealed a much higher sensitivity of tobacco 5-oxo-prolinase to these compounds than observed for the mammalian enzyme.
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