title: A novel alliinase from onion roots. Biochemical characterization and cDNA cloning.
abstract: We have purified a novel alliinase (EC 4.4.1.4) from roots of onion (Allium cepa L.). Two isoforms with alliinase activity (I and II) were separated by concanavalin A-Sepharose and had molecular masses of 52.7 (I) and 50.5 (II) kD on sodium dodecyl sulfate-polyacrylamide gel electrophoresis, and 51 (I) and 57.5 (II) kD by gel filtration fast-protein liquid chromatography. Isoform I had an isoelectric point of 9.3, while isoform II had isoelectric points of 7.6, 7.9, 8.1, and 8.3. The isoforms differed in their glycosylation. Both contained xylose/fucose containing complex-type N-linked glycans, and isoform II also contained terminal mannose structures. Both isoforms had activity with S-alk(en)yl-L-cysteine sulfoxides. Unlike other allium alliinases, A. cepa root isoforms had cystine lyase activity. We cloned a gene from A. cepa root cDNA and show that it codes for A. cepa root alliinase protein. Homology to other reported allium alliinase genes is 50%. The gene coded for a protein of mass 51.2 kD, with two regions of deduced amino acid sequence identical to a 25- and a 40-amino acid region, as determined experimentally. The A. cepa root alliinase cDNA was expressed mainly in A. cepa roots. The structure and function of the alliinase gene family is discussed.
authors.affiliation: New Zealand Institute for Crop and Food Research Limited, Private Bag 4704, Christchurch, New Zealand. jlancaster@xtra.co.nz
authors.forename: J E
authors.initials: JE
authors.lastname: Lancaster
authors.forename: M L
authors.initials: ML
authors.lastname: Shaw
authors.forename: M D
authors.initials: MD
authors.lastname: Joyce
authors.forename: J A
authors.initials: JA
authors.lastname: McCallum
authors.forename: M T
authors.initials: MT
authors.lastname: McManus
mesh_terms: D000595:Amino Acid Sequence; D001483:Base Sequence; D013437:Carbon-Sulfur Lyases / Q000235:genetics / Q000378:metabolism*; D003001:Cloning, Molecular; D017931:DNA Primers; D018076:DNA, Complementary; D008969:Molecular Sequence Data; D019697:Onions / Q000201:enzymology*; D018517:Plant Roots / Q000201:enzymology; D017386:Sequence Homology, Amino Acid
chemical_list: D017931:DNA Primers; D018076:DNA, Complementary; D013437:Carbon-Sulfur Lyases; C019243:alliin lyase