Functional properties of diapophytoene and related desaturases of C-30 andC-40 carotenoid biosynthetic pathways

The desaturation reactions Of C-30 carotenoids from diapophytoene to diapon eurosporene was investigated in vitro and by complementation in Escherichia coli. The expressed diapophytoene desaturase from Staphylococcus aureus in serts three double bonds in an FAD-dependent reaction. The enzyme is inhibi ted by diphenylamine. In the complementation experiment diapophytoene desat urase was able to convert C-40 phytoene to some extend but exhibited a high affinity to zeta -carotene. Comparison to the reaction of a phytoene desat urase from Rhodobacter capsulatus catalyzing a parallel three-step desatura tion sequence with the corresponding C-40 carotenes revealed that this desa turase can also convert C-30 diapophytoene. Other homologous bacterial C-40 carotene desaturases could also utilize C-30 substrates, including one typ e of zeta -carotene desaturase which converted diaponeurosporene to diapoly copene. Further complementation experiments including the diapophytoene syn thase gene from S. aureus revealed that the C-30 carotenogenic pathway is d etermined by this initial enzyme which is highly homologous to C-40 phytoen e synthases. (C) 2001 Elsevier Science BN. All rights reserved.