Substrate selectivity profiles expressed as catalytic efficiency, kcat/Km, of mutants Ghelix and GIMFhelix as well as of wild-type GST A1–1 and GST A4–4, with the following substrates: hexenal (black), hydroxyhexenal, HHE (gray), nonenal (hatched), and HNE (white). The kcat/Km values for GST A4–4 obtained with HHE and HNE were determined previously (13). The kinetic parameters for hexenal and nonenal are from Table 2, and for HHE and HNE as follows: GST A1–1, KmHNE = 0.047 ± 0.002 mM, kcatHNE = 2.4 ± 0.05 s-1; Ghelix, KmHNE = 0.047 ± 0.017 mM, kcatHNE = 6.3 ± 1.3 s-1; GIMFhelix, KmHHE = 0.39 ± 0.07 mM, kcatHHE = 42.9 ± 6.4 s-1, KmHNE = 0.011 ± 0.003 mM, kcatHNE = 11.6 ± 0.7 s-1; and GST A4–4 (13), KmHHE = 0.23 ± 0.05 mM, kcatHHE = 23 ± 3 s-1, KmHNE = 0.037 ± 0.004 mM, kcatHNE = 113 ± 4 s-1.