Regioselectivity of various mutants relative to castor WT (D) Δ9 desaturase with 14∶0-ACP substrate. (A) The regioselectivity of the quadruple mutant (Arg333Lys, Leu337Val, Arg340Lys, Arg344Lys). The quintuple mutant is the quadruple mutant plus Asp280Lys (K), and the single mutant Asp280Lys (K) is also shown. (B) A comparison of the regioselectivity for WT (D) and substitutions as indicated at position 280, Glu (E), Met (M), Ile, (I), Lys (K), Arg (R), and the double mutant Asp280Arg, Ala284Arg (RR).