Functional properties of diapophytoene and related desaturases of C30 and C40 carotenoid biosynthetic pathways

The desaturation reactions Of C-30 carotenoids from diapophytoene to diaponeurosporene was investigated in vitro and by complementation in Escherichia coli. The expressed diapophytoene desaturase from Staphylococcus aureus inserts three double bonds in an FAD-dependent reaction. The enzyme is inhibited by diphenylamine. In the complementation experiment diapophytoene desaturase 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 desaturase from Rhodobacter capsulatus catalyzing a parallel three-step desaturation sequence with the corresponding C-40 carotenes revealed that this desaturase can also convert C-30 diapophytoene. Other homologous bacterial C-40 carotene desaturases could also utilize C-30 substrates, including one type of zeta -carotene desaturase which converted diaponeurosporene to diapolycopene. Further complementation experiments including the diapophytoene synthase gene from S. aureus revealed that the C-30 carotenogenic pathway is determined by this initial enzyme which is highly homologous to C-40 phytoene synthases. (C) 2001 Elsevier Science BN. All rights reserved.