title: Calcium modulates membrane association, positional specificity, and product distribution in dual positional specific maize lipoxygenase-1.
abstract: This study investigates how calcium modulates the properties of dual positional specific maize lipoxygenase-1, including its interaction with substrate, association with subcellular membrane and alteration of product distribution. Bioinformatic analyses identified Asp(38), Glu(127) and Glu(201) as putative calcium binding residues and Leu(37) as a flanking hydrophobic residue also potentially involved in calcium-mediated binding of the enzyme to subcellular membranes. Asp(38) and Leu(37) were shown to be important but not essential for calcium-mediated association of maize lipoxygenase-1 to subcellular membranes in vitro. Kinetic studies demonstrate that catalytic efficiency (Vmax/Km) shows a bell-shaped dependence on log of the molar ratio of substrate to unbound calcium. Calcium also modulates product distribution of the maize lipoxygenase-1 reaction, favoring 13-positional specificity and increasing the relative amount of (E,Z)-isomeric products. The results suggest that calcium regulates the maize lipoxygenase-1 reaction by binding to substrate, and by promoting binding of substrate to enzyme and association of maize lipoxygenase-1 to subcellular membranes.
authors.affiliation: Department of Molecular Biotechnology and Kumho Life Science Laboratory, College of Agriculture and Life Sciences, Chonnam National University, Gwangju 500-757, Republic of Korea.
authors.forename: Kyoungwon
authors.initials: K
authors.lastname: Cho
authors.affiliation: Department of Molecular Biotechnology and Kumho Life Science Laboratory, College of Agriculture and Life Sciences, Chonnam National University, Gwangju 500-757, Republic of Korea.
authors.forename: Jihoon
authors.initials: J
authors.lastname: Han
authors.affiliation: Organization for Educational Initiatives, University of Tsukuba, 1-1-1 Tennoudai, Tsukuba, Ibaraki 305-8577, Japan.
authors.forename: Randeep
authors.initials: R
authors.lastname: Rakwal
authors.affiliation: Department of Molecular Biotechnology and Kumho Life Science Laboratory, College of Agriculture and Life Sciences, Chonnam National University, Gwangju 500-757, Republic of Korea. Electronic address: oshan@chonnam.ac.kr.
authors.forename: Oksoo
authors.initials: O
authors.lastname: Han
mesh_terms: D000595:Amino Acid Sequence; D002118:Calcium / Q000378:metabolism*; D002736:Chloroplasts / Q000235:genetics / Q000378:metabolism / Q000648:ultrastructure; D007700:Kinetics; D008084:Lipoxygenase / Q000032:analysis / Q000235:genetics / Q000378:metabolism*; D008969:Molecular Sequence Data; D030821:Plants, Genetically Modified; D021381:Protein Transport; D013379:Substrate Specificity; D003313:Zea mays / Q000166:cytology / Q000201:enzymology* / Q000235:genetics / Q000378:metabolism
chemical_list: D008084:Lipoxygenase; D002118:Calcium
keywords: Calcium; Dual positional specificity; Linoleic acid; Lipoxygenase; Monocot