The three enzymes were shown to catalyze the final step in the biosynthesis of the GSL core structure; the sulfation of desulfoGSLs (dsGSs). They accept a broad range of desulfoGSLs as substrates. In a competitive situation; AtST5a (SOT16) clearly prefers tryptophan and phenylalanine-derived desulfoGSLs whereas long chain desulfoGSLs derived from methionine are the preferred substrates of SOT17 and SOT18 (Piotrowski et al. 2004)