title: An electron paramagnetic resonance method for quantification of copper isotopes in proteins: application to a mixed-isotope derivative of laccase.
abstract: We have developed a method of denaturing a copper-containing protein and sequestering the copper in the form of the bis(acetylacetonato)copper(II) complex. Because of the excellent resolution of the hyperfine structure in the resulting EPR spectrum, the method is useful for determining the 65Cu/63Cu isotope ratio in proteins such as tree laccase. Here we analyzed a mixed isotope sample prepared by reconstituting 63Cu-enriched type 2-depleted laccase with 65Cu(I) and found that it contained only 25% 65Cu. This proves that reconstitution of the type 2 copper is possible under conditions that permit little or no exchange between resident copper and the external pool. However, exchange does occur under reducing conditions when we expose the holoprotein to a large excess of exogenous copper.
authors.affiliation: Department of Chemistry, Purdue University, West Lafayette, Indiana 47907-1393, USA.
authors.forename: C
authors.initials: C
authors.lastname: Miller
authors.forename: J
authors.initials: J
authors.lastname: Fajardo
authors.forename: W E
authors.initials: WE
authors.lastname: Antholine
authors.forename: D R
authors.initials: DR
authors.lastname: McMillin
mesh_terms: D001665:Binding Sites; D002411:Cation Exchange Resins / Q000737:chemistry; D002614:Chelating Agents / Q000737:chemistry; D003300:Copper / Q000032:analysis* / Q000737:chemistry; D004578:Electron Spin Resonance Spectroscopy / Q000379:methods*; D007553:Isotope Labeling; D007554:Isotopes; D042845:Laccase; D010088:Oxidoreductases / Q000737:chemistry*; D010422:Pentanones / Q000737:chemistry; D011489:Protein Denaturation; D012117:Resins, Synthetic; D014197:Trees / Q000201:enzymology
chemical_list: D002411:Cation Exchange Resins; D002614:Chelating Agents; D007554:Isotopes; D010422:Pentanones; D012117:Resins, Synthetic; C024997:Chelex 100; C008790:acetylacetone; D003300:Copper; D010088:Oxidoreductases; D042845:Laccase