3,4-dihydroxyphenylalanine is oxidized by phenoxyl radicals of hydroxycinnamic acid esters in leaves of Vicia faba L
1998
Takahama, U. (Kyushu Dental Univ., Kitakyushu, Fukuoka (Japan)) | Oniki, T.
Mechanisms of oxidation of 3,4-dihydroxyphenylalanine (dopa) in leaves of Vicia faba have not yet been elucidated in details. The author hypothesized its xidation by radicals of hydroxycinnamic acid esters that were generated by a peroxidase-dependent reaction in acuoles. The results obtained in this study were followings. 1) Vacuolar peroxidase isolated from the leaves oxidized dopa more slowly than 4-coumaric and caffeic acid esters isolated from the leaves. 2) The hydroxycinnamic acid esters enhanced peroxidase-dependent oxidation of dopa and dopa suppressed their oxidation. 3) Degree of the enhancement was roughly correlated with rates of the oxidation of hydroxycinnamic: acid esters. 4) The hydroxycinnamic acid esters increased levers of dopa radical in the presence of peroxidase. 5) In protoplasts of mesophyll cells of V. faba, hydrogen peroxide-induced oxidation of dopa was faster than that of 4-coumaric acid and caffeic acid esters. These results support the above hypothesis that dopa in vacuoleS is oxidized by phenoxyl radicals of hydroxycinnamic acid esters that are generated by vacuolar peroxidase
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