3, 4-Dihydroxyphenylalanine is oxidized by phenoxyl radicals of hydroxycinnamic acid esters in leaves ofVicia faba L |
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Authors: | Umeo Takahama Takayuki Oniki |
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Institution: | (1) Kyushu Dental College, 803-8580 Kitakyushu, Japan |
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Abstract: | Mechanisms of oxidation of 3,4-dihydroxyphenylalanine (dopa) in leaves ofVicia faba have not yet been elucidated in details. The author hypothesized its oxidation by radicals of hydroxycinnamic acid esters
that were generated by a peroxidase-dependent reaction in vacuoles. 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 levels of dopa radical in the presence of peroxidase. 5) In protoplasts of mesophyll cells ofV. 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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Keywords: | Dopa Hydroxycinnamic acids Mechanism of oxidation of dopa Mesophyll cell protoplasts Vacuolar peroxidase Vicia faba |
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