Sequence comparison between the oleate hydroxylase (FAH12) and the oleate desaturase (FAD2) in castor. The FAD2 is four amino acids shorter than the FAH12 at the N-terminus (shown by dashes). Identical amino acids are indicated by dots. The three regions containing histidine residues conserved among fatty acid desaturases are shown in red letters. The 8 amino acids in bold faces have been shown to be involved in determining the catalytic outcome of the desaturation/hydroxylation reactions .