Du 640 series beckman spectrophotometer

The xanthine oxidase system was used to determine the O₂^∙− scavenging capacity of the Tilia extracts. Levels of O₂^∙− in the assay system and xanthine oxidase activity were measured by an NBT reduction using a DU-640 series Beckman spectrophotometer. This system can be used to test the O₂^∙− scavenging capacity only when the samples do not interfere with xanthine oxidase activity. A compound with O₂^∙− scavenging capacity should decrease the NBT reduction without interfering with the xanthine oxidase activity measured as uric acid production. A total of 800 μL of the following reaction mixture was mixed with 100 μL of different concentrations of Tilia extracts: 90 μM xanthine, 16 mM Na₂CO₃, 22.8 μM NBT, and 18 mM phosphate buffer (pH 7.0). The reaction was started by the addition of 100 μL of xanthine oxidase (168 U/L). The optical density was recorded at 295 nm for uric acid production and 560 nm for O₂^∙− in the assay system [15 ]. The scavenging percentage was obtained from the optical density at 560 nm. NDGA (0, 1, 2, 3.02, and 8 μg/mL) was used as a standard for O₂^∙− scavenging in this assay.

The superoxide radicals (O₂⁻) were generated through the system xanthine oxidase [29 (link)]. O₂⁻ in the assay system and xanthine oxidase activity were measured as NBT reduction using a DU-640 series Beckman spectrophotometer. 800 μL of the following reaction mixtures: 90 μM xanthine, 16 mM Na₂CO₃, 22.8 μM NBT, and 18 mM phosphate buffer (pH 7.0) was mixed with 100 μL of different concentrations of H. inuloides metabolites. The reaction was started by the addition of 100 μL of xanthine oxidase (168 U/L). Optical density was registered both at 295 (for uric acid production) and at 560 nm (for O₂⁻ in the assay system). The absorbance was determined using a Beckman DU640 Spectrophotometer (Beckman Coulter, Inc. California, USA).