Sterol Biosynthesis in Arabidopsis.
The pathway from cycloartenol to the Δ22-sterols is shown. 24-Methyl sterols are a mixture of (24R)- and (24S)-epimers of campesterol (Schaller, 2003). The Δ22-desaturases catalyze the C22-desaturation reaction to yield stigmasterol, crinosterol, and brassicasterol from their immediate precursors. Dashed arrows indicate several enzymatic steps not shown here.