title: A proof for substitution of endogenous iron (II) in lipoxygenase by exogenous Cu2+.
abstract: Soybean lipoxygenase (LOX) contains endogenous iron (II) at the active site, which is important for the enzyme activity. The activity of LOX can be accelerated by some exogenous metal ions including Cu2+. However, the mechanism of the activity improvement caused by exogenous metal ions remains unclear, not only for LOX but for most other metalloenzymes. Meanwhile, the possibility that exogenous metal ions can displace endogenous iron (II) is still in discussion for a lack of a direct and quantitative proof. In this paper, a quantitative proof of replacing iron (II) inside LOX by exogenous Cu2+ was provided, simply using UV-Vis spectrometry with two indicators p-carboxylantipyrylazo and 9-(4-carboxyphenyl)-2,3,7-trihydroxyl-6-fluorine. A 0.56 microM free iron (II) was observed in the bulk solution after incubating 9.45 microM Cu2+ with 16.10 microM LOX at 20 degrees C for 5 min, which is in coincidence with the decrement of Cu2+ in the bulk solution (0.53 microM), implying that iron (II) was replaced by Cu2+.
authors.affiliation: School of Chemical and Material Engineering, Jiangnan University, 1800 Lihu Avenue, Wuxi, Jiangsu 214122, China.
authors.forename: Yan
authors.initials: Y
authors.lastname: Cai
authors.forename: Hong
authors.initials: H
authors.lastname: Xu
authors.forename: Yongmei
authors.initials: Y
authors.lastname: Xia
authors.forename: Yafen
authors.initials: Y
authors.lastname: Su
authors.forename: Yun
authors.initials: Y
authors.lastname: Fang
mesh_terms: D020134:Catalytic Domain; D003300:Copper / Q000737:chemistry*; D007501:Iron / Q000737:chemistry*; D007700:Kinetics; D008084:Lipoxygenase / Q000737:chemistry*; D011485:Protein Binding; D030262:Soybean Proteins / Q000737:chemistry*; D013025:Glycine max / Q000737:chemistry / Q000201:enzymology*
chemical_list: D030262:Soybean Proteins; D003300:Copper; D007501:Iron; D008084:Lipoxygenase