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

The desaturation reactions of C30 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 C40 phytoene to some extend but exhibited a high affinity to ζ-carotene. Comparison to the reaction of a phytoene desaturase from Rhodobacter capsulatus catalyzing a parallel three-step desaturation sequence with the corresponding C40 carotenes revealed that this desaturase can also convert C30 diapophytoene. Other homologous bacterial C40 carotene desaturases could also utilize C30 substrates, including one type of ζ-carotene desaturase which converted diaponeurosporene to diapolycopene. Further complementation experiments including the diapophytoene synthase gene from S. aureus revealed that the C30 carotenogenic pathway is determined by this initial enzyme which is highly homologous to C40 phytoene synthases.