Dataset Information

Optimized DPPH assay in a detergent-based buffer system for measuring antioxidant activity of proteins.

ABSTRACT: The 1,1-Diphenyl-2-picryl-hydrazyl (DPPH) assay is well established for the in vitro determination of antioxidant activity in food and biological extracts. The standard DPPH assay uses methanol or ethanol as solvents, or buffered alcoholic solutions in a ratio of 40%/60% (buffer/alcohol, v/v) to keep the hydrophobic hydrazyl radical and phenolic test compounds soluble while offering sufficient buffering capacity at different pHs tested. Following this protocol, we were unable to keep proteinaceous antioxidants soluble at different pHs to test for their antioxidant activity. Thus, the assay protocol was modified as follows to improve its utility: Non-ionic detergents were added to keep the DPPH radical soluble and to provide a mild and non-denaturing environment for the antioxidant protein.Maximal concentration of DPPH was limited to 100 μM to stay within the sensitivity range of the detector at the given wavelength (515 nm) and to increase the dynamic range of the assay.0.1 M citrate phosphate buffer was introduced to prevent experimental artifacts due to changing buffer compositions at different pHs.

SUBMITTER: Nicklisch SC

PROVIDER: S-EPMC4268772 | biostudies-literature |

REPOSITORIES: biostudies-literature

ACCESS DATA

Similar Datasets

Project description:Studies have shown that modification of critical cysteine residues in proteins leads to the regulation of protein function. These modifications include disulfide bond formation, glutathionylation, sulfenic and sulfinic acid formation, and S-nitrosation. The biotin switch assay was developed to specifically detect protein S-nitrosation (S. R. Jaffrey et al., Nat. Cell Biol. 3:193-197; 2001). In this assay, proteins are denatured with SDS in the presence of methyl methane thiosulfonate (MMTS) to block free thiols. After acetone precipitation or Sephadex G25 separation to remove excess MMTS, HPDP-biotin and 1 mM ascorbate are added to reduce the S-nitrosothiol bonds and label the reduced thiols with biotin. The proteins are then separated by nonreducing SDS PAGE and detected using either streptavidin-HRP or anti-biotin-HRP conjugate. Our examination of this labeling scheme has revealed that the extent of labeling depends on the buffer composition and, importantly, on the choice of metal-ion chelator (DTPA vs EDTA). Unexpectedly, using purified S-nitrosated albumin, we have found that "contaminating" copper is required for the ascorbate-dependent degradation of S-nitrosothiol; this is consistent with the fact that ascorbate itself does not rapidly reduce S-nitrosothiols. Removal of copper from buffers by DTPA and other copper chelators preserves approximately 90% of the S-nitrosothiol, whereas the inclusion of copper and ascorbate completely eliminates the S-nitrosothiol in the preparation and increases the specific biotin labeling. These biotin switch experiments were confirmed using triiodide-based and copper-based reductive chemiluminescence. Additional modifications of the assay using N-ethylmaleimide for thiol blockade, ferricyanide pretreatment to stabilize S-nitrosated hemoglobin, and cyanine dye labeling instead of biotin are presented for the measurement of cellular and blood S-nitrosothiols. These results indicate that degradation of S-nitrosothiol in the standard biotin switch assay is metal-ion dependent and that experimental variability in S-nitrosothiol yields using this assay occurs secondary to the inclusion of metal-ion chelators in reagents and variable metal-ion contamination of buffers and labware. The addition of copper to ascorbate allows for a simple assay modification that dramatically increases sensitivity while maintaining specificity.

Dataset Information

Optimized DPPH assay in a detergent-based buffer system for measuring antioxidant activity of proteins.

Similar Datasets

OmicsDI is part of the ELIXIR infrastructure

Tweets