Abstract
Stigmasterol, containing a double bond at the C-22 position in the side chain, is one of the major constituents of plant sterols and biosynthesized by the C-22 desaturation of β-sitosterol. However, the gene encoding the C-22 desaturase has not been identified from higher plants. In yeast, cytochrome P450 (CYP61) has been known as the sterol C-22 desaturase, and the CYP710A family has the highest homology (28%) to CYP61 among plant P450s. Thus, we presumed that CYP710A is the plant sterol C-22 desaturase, and investigated the in vitro activity. Recombinant CYP710As expressed in a baculovirus/insect cell system exhibited a notable C-22 desaturase activity with β-sitosterol to produce stigmasterol. As brassicasterol occurs specifically in Brassicaceae family plants and is biosynthesized from 24-epi-campesterol by the C-22 desaturation, we examined the substrate specificity of Arabidopsis CYP710A1~A4. Each CYP710A exhibited the strict substrate specificity for either β-sitosterol or 24-epi-campesterol.
