Quinone compounds are able to replace molecular oxygen as terminal electron acceptor in phytoene desaturation in chromoplasts of Narcissus pseudonarcissus L.

The desaturation of phytoene to zeta-carotene and of zeta-carotene to lycopene employs molecular oxygen as the terminal electron acceptor. 2,3,5,6-Tetramethyl-1,4-benzoquinone (duroquinone) and other artificial quinones are able to replace oxygen, which demonstrates that oxygen does not act in a mixed-function oxygenase-like mechanism at the desaturase itself, but at a spatially separate site. Evidence for additional redox elements mediating between desaturase and oxygen is presented.