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FAD is a further essential cofactor of the NAD(P)H and O 2 ‐dependent zeaxanthin‐epoxidase
Author(s) -
Büch Karen,
Stransky Harald,
Hager Achim
Publication year - 1995
Publication title -
febs letters
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.593
H-Index - 257
eISSN - 1873-3468
pISSN - 0014-5793
DOI - 10.1016/0014-5793(95)01243-9
Subject(s) - violaxanthin , thylakoid , nad+ kinase , cofactor , biochemistry , chemistry , flavin group , xanthophyll , antheraxanthin , enzyme , stereochemistry , zeaxanthin , chloroplast , photosynthesis , lutein , gene , carotenoid
In chloroplasts of plants the xanthophyll cycle is suggested to function as a protection mechanism against photodamage. Two enzymes catalyze this cycle. One of them, violaxanthin de‐epoxidase, transforms violaxanthin (Vio) to zeaxanthin (Zea) via antheraxanthin (Anth) and is bound to the lumenal surface of the thylakoid vesicles, when being in its active state. The other enzyme, Zea‐epoxidase, is responsible for the backward reaction (Zea → Anth → Vio) and is active at the stromal side of the thylakoid. For the epoxidation of Zea this enzyme requires NAD(P)H and O 2 as cosubstrates. Using isolated thylakoid membranes we found that FAD enhances the epoxidase activity (decrease of apparent K m for NAD(P)H and two‐fold increase of V max ). The flavin functions as a third cofactor which is partially lost during the isolation procedure of thylakoids. Other flavins, such as FMN or riboflavin are without effect. The involvement of FAD in the enzymatic reaction is also demonstrated by the inhibitory action of diphenyleneiodoniumchloride (DPI) (IC 50 = 2.3 μ M), a compound that blocks the reoxidation of reduced flavins within enzymes. The Zea‐epoxidase is a multicomponent enzyme system which can be classified as FAD‐containing, NAD(P)H‐ and O 2 ‐dependent monooxygenase that is able to epoxidize 3‐hydroxy β‐ionone rings of xanthophylls in the 5,6 position.