The purification and characterization of fatty acid hydroperoxide lyase in sunflower

Two fatty acid hydroperoxide lyases (HPO lyase I and II) were purified to apparent homogeneity from etiolated hypocotyls of sunflower (Helianthus annuus L.) by a combination of ion-exchange, hydrophobic interaction, and gel filtration chromatography. The two HPO lyases were separated during the hydrophobic interaction chromatography step, with HPO lyase I more hydrophilic than HPO lyase II. The estimated Mr of both native HPO lyases was determined by gel filtration to be 200 000, and SDS-PAGE in the presence of 100 mM dithiothreitol showed that the enzyme was composed of a single 53 kDa peptide, suggesting that the enzyme exists as a tetramer in vivo. HPO lyase was also abundant in the cotyledons and green leaves. HPO lyases I and II from hypocotyl metabolized 13-hydroperoxylinoleic acid and 13-hydroperoxylinolenic acid to the same extent, but the green leaf enzyme was more than ten-fold more active with 13-hydroperoxylinolenic acid than 13-hydroperoxylinoleic acid. A difference spectrum between CO-bound and CO-unbound dithionite-reduced HPO lyase I showed an absorbance maximum at 452 nm, indicating that it was a cytochrome P450-type enzyme. The activities of HPO lyase I and II were significantly inhibited by nordihydroguaiaretic acid, sulfhydryl reagents, and piperonylbutoxide, which is a cytochrome P450 inhibitor.