Part of the xanthophyll (or violaxanthin) cycle for controlling the concentration of zeaxanthin in chloroplasts. Catalyzes the two-step mono de-epoxidation reaction. Stereospecific for all-trans xanthophylls. Zeaxanthin induces the dissipation of excitation energy in the chlorophyll of the light-harvesting protein complex of photosystem II. all-trans-violaxanthin + 2 L-ascorbate = all-trans-zeaxanthin + 2 H2O + 2 L-dehydroascorbate Irreversibly inhibited by DTT and iodoacetamide at pH 5.7 or pH 5.2, but not at pH 7.2 (Ref.5, Ref.3). Regulated through Ca(2+) gating of H(+) flux at the CFoH(+) channel (PubMed:16228481). Requires the presence of lipids forming reverse hexagonal structures such as monogalactosyldiacylglyceride (MGDG) or phosphatidylethanolamine (PubMed:15078086). A negative curvature elastic stress in the thylakoid lipid bilayer is required for VDE1 activity (PubMed:17618598). KM for ascorbate increased when H-245, H-248, H-291 or H-297 are mutated. Optimum pH is 5.0. Binds to the thylakoid membrane at pH 5.2 and is released in the lumen at pH 7.2. Disulfide bonds. Reduction of the disulfides results in loss of a rigid structure, a decrease in thermal stability of 15 degrees Celsius and a loss of activity. The amount of VDE in vivo is estimated to be 1 molecule per 20-100 electron transport chains. Belongs to the calycin superfamily. Lipocalin family.