zeaxanthin epoxidase

A flavoprotein (FAD) that is active under conditions of low light. Along with EC 1.10.99.3, violaxanthin de-epoxidase, this enzyme forms part of the xanthophyll (or violaxanthin) cycle, which is involved in protecting the plant against damage by excess light. It will also epoxidize lutein in some higher-plant species. Reaction: zeaxanthin + 2 NAD(P)H + 2 H+ + 2 O2 = violaxanthin + 2 NAD(P)+ + 2 H2O (overall reaction); (1a) zeaxanthin + NAD(P)H + H+ + O2 = antheraxanthin + NAD(P)+ + H2O; (1b) antheraxanthin + NAD(P)H + H+ + O2 = violaxanthin + NAD(P)+ + H2O