Description
Catalase (CAT, EC 1.11.1.6) is widely found in animals, plants, microorganisms, and cultured cells. It is the primary H₂O₂-scavenging enzyme and plays a crucial role in the reactive oxygen species (ROS) scavenging system. H₂O₂ has a characteristic absorption peak at 240 nm. CAT decomposes H₂O₂, causing the absorbance of the reaction solution at 240 nm to decrease over time. The CAT activity can be calculated based on the rate of change in absorbance.Component50TStorageExtraction Buffer60 mL2-8℃Working Solution60 mL2-8℃User-Prepared Instruments and ReagentsUV spectrophotometer, benchtop centrifuge, adjustable pipettes, 1 mL quartz cuvette, mortar, ice, and distilled water.Experimental Procedure1. Crude Enzyme Extract Preparation1.1 Bacterial/Cell SamplesCollect bacteria or cells into a centrifuge tube, centrifuge, and discard the supernatant. Use a bacteria/cell count (10⁴) to Extraction Buffer volume (mL) ratio between 500:1 and 1000:1 (recommended: 5 million bacteria/cells in 1 mL Extraction Buffer). Disrupt the bacteria or cells by sonication (ice bath, power 20% or 200W, pulse 3s on, 10s off, repeat 30 times). Centrifuge at 8,000 g, 4°C for 10 minutes. Collect the supernatant and keep it on ice for assay.1.2 Tissue SamplesUse a tissue mass (g) to Extraction Buffer volume (mL) ratio between 1:5 and 1:10 (recommended: weigh approx. 0.1 g tissue, add 1 mL Extraction Buffer). Homogenize in an ice bath. Centrifuge at 8,000 g, 4°C for 10 minutes. Collect the supernatant and keep it on ice for assay.1.3 Serum (Plasma) SamplesAssay directly.2. Assay Steps2.1 Preheat the spectrophotometer for at least 30 minutes. Set the wavelength to 240 nm. Zero the instrument with distilled water.2.2 Before assay, incubate the CAT Working Solution in a water bath at 37°C (for mammals) or 25°C (for other species) for 10 minutes.2.3 Add 35 µL of sample and 1 mL of Working Solution into a 1 mL quartz cuvette. Mix well and immediately measure the initial absorbance at 240 nm (A₁). Measure the absorbance again after 1 minute (A₂). Calculate ΔA = A₁ - A₂.3. CAT Activity Calculation3.1 Calculation of CAT Activity in Serum (Plasma)Unit Definition: One unit of enzyme activity is defined as the amount that catalyzes the degradation of 1 nmol of H₂O₂ per minute per milliliter of serum (plasma).Derived Formula:CAT Activity (nmol/min/mL) = [ΔA × Vtotal reaction÷ (ε × d) × 10⁹] ÷ Vsample÷ TSimplified Formula:CAT Activity (nmol/min/mL) = 678 × ΔA3.2 Calculation of CAT Activity in Tissues, Bacteria, or Cells(1) Based on Sample Protein ConcentrationUnit Definition: One unit of enzyme activity is defined as the amount that catalyzes the degradation of 1 nmol of H₂O₂ per minute per milligram of tissue protein.Derived Formula:CAT Activity (nmol/min/mg prot) = [ΔA × Vtotal reaction÷ (ε × d) × 10⁹] ÷ (Vsample× Cpr) ÷ TSimplified Formula:CAT Activity (nmol/min/mg prot) = 678 × ΔA ÷ Cpr(2) Based on Sample Fresh WeightUnit Definition: One unit of enzyme activity is defined as the amount that catalyzes the degradation of 1 nmol of H₂O₂ per minute per gram of tissue.Derived Formula:CAT Activity (nmol/min/g fresh weight) = [ΔA × Vtotal reaction÷ (ε × d) × 10⁹] ÷ (W × Vsample÷ Vtotal sample) ÷ TSimplified Formula:CAT Activity (nmol/min/g fresh weight) = 678 × ΔA ÷ W(3) Based on Bacterial or Cell DensityUnit Definition: One unit of enzyme activity is defined as the amount that catalyzes the degradation of 1 nmol of H₂O₂ per minute per 10⁴ bacteria or cells.Derived Formula:CAT Activity (nmol/min/10⁴ cells) = [ΔA × Vtotal reaction÷ (ε × d) × 10⁹] ÷ (500 × Vsample÷ Vtotal sample) ÷ TSimplified Formula:CAT Activity (nmol/min/10⁴ cells) = 1.356 × ΔAParameter Definitions:1.ΔA: Change in absorbance (A₁ - A₂)2.Vtotal reaction: Total reaction volume (1.035 × 10⁻³ L)3.ε: Molar extinction coefficient of H₂O₂ (4.36 × 10⁴ L/mol/cm)4.d: Light path length of the cuvette (1 cm)5.10⁹: Unit conversion factor (1 mole = 10⁹ nmoles)6.Vsample: Volume of sample added to the reaction (0.035 mL)7.T: Reaction time (1 min)8.Cpr: Sample protein concentration (mg/mL)9.W: Sample weight (g)10.Vtotal sample: Total volume of extraction buffer added (1 mL)11.500: Total number of bacteria or cells (5 million)Precautions1.Before formal testing, it is essential to perform a preliminary test with 2-3 samples expected to have significant differences.2.This product is for research use only. Not for use in clinical diagnosis.Frequently Asked Questions (FAQ)Q: What should I do if I get a negative value?A: Check if bubbles formed during the reaction. Excessive bubbling indicates very high enzyme activity, and bubbles can interfere, causing negative values. Try diluting the sample 10-fold with Extraction Buffer and re-assaying. If no bubbles form (with diluted sample or original reaction) and a small negative value persists, it indicates that the enzyme activity in this sample is below the detection limit