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A plasma membrane‐bound enzyme oxidizes l ‐tryptophan to indole‐3‐acetaldoxime
Author(s) -
LudwigMüller Jutta,
Hilgenberg Willy
Publication year - 1988
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.1399-3054.1988.tb00627.x
Subject(s) - tryptophan , membrane , chemistry , chromatography , pisum , helianthus annuus , biochemistry , nicotiana tabacum , sunflower , biology , amino acid , horticulture , gene
The in vitro conversion of [ 14 C]‐tryptophan to [ 14 C]‐indole‐3‐acetaldoxime (IAOX) by microsomal membranes of Chinese cabbage (Brassica campestris ssp. pekinensis cv. Granat) has been studied. The reaction product was identified by thin‐layer chromatography (TLC) and high performance liquid chromatography (HPLC). Furthermore. IAOX was identified as an endogenous compound of Chinese cabbage by mass spectroscopy. The tryptophan‐oxidizing enzyme (TrpOxE) was characterized. MnCl 2 was required as cofactor, H 2 O 2 , and 2,4‐dichlorophenol (DCP) stimulated the reaction. The enzyme showed a pH optimum at pH 8–9 and a K m for l ‐tryptophan of 20 μ M . The membranes containing TrpOxE activity were identified as plasma membranes by means of aqueous polymer two‐phase partitioning. The TrpOxE from Chinese cabbage was purified 3‐fold from plasma membranes by solubilization followed by (NH 4 ) 2 SO 4 ‐fractionation, affinity‐chromatography with concanavalin A, and native gel electrophoresis. Enzyme activity was reduced by a tunicamycin pretreatment. Several other plant species, e.g. maize (Zea mays L. Inrakorn), sunflower (Helianthus annuus L. cv. Hohes Sonnengold), tobacco (Nicotiana tabacum L. cv. White Burley), and pea (Pisum sativum L. cv. Krombeck) showed a similar conversion of [ 14 C]‐tryptophan to [ 14 C]‐IAOX by phase‐partitioned plasma membranes.