title: U-2012: An improved Lowry protein assay, insensitive to sample color, offering reagent stability and enhanced sensitivity.
abstract: Traditional colorimetric protein assays such as Biuret, Lowry, and modified Lowry (U-1988) are unsuitable for colored biological samples. Here we describe an improved Lowry protein assay (U-2012), which utilizes stable reagents and offers enhanced sensitivity over the U-1988 assay. U-2012 circumvents interference from colored pigments and other substances (for example sugars) bound to perchloric acid (PCA) precipitated proteins by hydrogen peroxide (H2O2) induced oxidation at 50°C. Unused hydrogen peroxide is neutralized with sodium pyruvate before protein estimation for a stable end color. The U-2012 assay is carried out on the PCA precipitated protein pellet after neutralization (with Na2CO3 plus NaOH), solubilization (in Triton-NaCl), decolorization (by H2O2) and pyruvate treatment. Protein contents in red wine and homogenates of beetroot and blueberry are calculated from standard curves established for various proteins and generated using a rectangular hyperbola with parameters estimated with Microsoft Excel's Solver add-in. The U-2012 protein assay represents an improvement over U-1988 and gives a more accurate estimation of protein content.
authors.affiliation: Plant & Food Research Ruakura, Private Bag 3230, Hamilton 3240, New Zealand. girish.upreti@plantandfood.co.nz
authors.forename: Girish C
authors.initials: GC
authors.lastname: Upreti
authors.forename: Yanming
authors.initials: Y
authors.lastname: Wang
authors.forename: Alona
authors.initials: A
authors.lastname: Finn
authors.forename: Abigail
authors.initials: A
authors.lastname: Sharrock
authors.forename: Nicholas
authors.initials: N
authors.lastname: Feisst
authors.forename: Marcus
authors.initials: M
authors.lastname: Davy
authors.forename: Robert B
authors.initials: RB
authors.lastname: Jordan
mesh_terms: D027461:Beta vulgaris; D029798:Blueberry Plants; D011232:Chemical Precipitation; D002623:Chemistry Techniques, Analytical / Q000379:methods*; D010472:Perchlorates / Q000737:chemistry; D010860:Pigments, Biological; D010940:Plant Proteins / Q000032:analysis*; D012680:Sensitivity and Specificity; D014920:Wine
chemical_list: D010472:Perchlorates; D010860:Pigments, Biological; D010940:Plant Proteins