Peroxidases are a class of enzymes that catalyze the oxidation of various organic and inorganic substrates. One of the most well-established, perhaps, is horseradish peroxidase (HRP). HRP is a robust ~40 kDa enzyme widely employed as a label in ELISA, immunoassays, Western blotting, and immunohistochemistry applications. HRP catalyzes the hydrogen peroxide-dependent oxidation of chromogenic and fluorogenic substrates to generate quantitative absorbance or fluorescence signals, respectively; luminol-based chemiluminescent reagents are also commonly used. AAT Bioquest's offers a complete selection of peroxidase activity assay kits, substrates, and related reagents, such as stop solutions, for a diverse range of applications and instrument platforms.

The Amplite® product line offers complete, ready-to-use assay kits designed for direct quantification of peroxidase enzyme activity and characterization of peroxidase-conjugated detection reagents. Each kit includes optimized buffers, hydrogen peroxide, substrates, and stopping solutions in stoichiometric ratios to maximize accuracy and reproducibility. The kits are available in colorimetric, fluorimetric, and luminometric formats with performance validated across standard 96-well and 384-well microplate platforms.

Catalase is a common antioxidant heme-containing redox enzyme found in nearly all living organisms exposed to oxygen. The enzyme is concentrated in peroxisome subcellular organelles and plays a critical role in preventing the excessive buildup of hydrogen peroxide, a toxic product of normal aerobic metabolism and pathogenic ROS production. By catalyzing the decomposition of H₂O₂ to water and oxygen, catalase protects cells from oxidative damage.

Amplite® Fluorimetric Catalase Assay Kit provides a quick and sensitive method for measuring catalase activity. The assay uses Amplite® Red substrate, which reacts with H₂O₂ to generate a red fluorescent product. The reduction in fluorescence intensity is proportional to catalase activity. The kit can detect as little as 30 mU/mL catalase in a 100 µL reaction volume.

Glutathione peroxidase (GPx) is an enzyme family with peroxidase activity that protects organisms from oxidative damage. GPx catalyzes the reduction of hydrogen peroxide and organic hydroperoxides to their corresponding alcohols using glutathione (GSH) as a reducing agent. Altered glutathione peroxidase levels correlate with many diseases including cancer, diabetes, and cardiovascular conditions.

Amplite® Fluorimetric Glutathione Peroxidase Assay Kit measures GPx activity through a coupled enzymatic reaction. GSH is oxidized to GSSG by GPx, then recycled by glutathione reductase and NADPH. The generated NADP⁺ is detected using Quest Fluor™ NADP sensor, enabling detection of as little as 1.25 mU/mL glutathione peroxidase.

Myeloperoxidase (MPO) is a green hemoprotein most abundantly present in neutrophils and monocytes. This 150 kDa dimeric enzyme catalyzes the reaction of hydrogen peroxide with halide ions to form cytotoxic acids and intermediates, playing an important role in the oxygen-dependent killing of tumor cells and microorganisms. MPO is a sensitive biomarker for neutrophil activation and inflammatory response.

Amplite® Fluorimetric Myeloperoxidase Assay Kit uses Amplite® Red substrate for dual-mode detection (fluorimetric or colorimetric). The kit can detect as little as 0.1 mU/mL myeloperoxidase and is suitable for high-throughput screening of MPO inhibitors.

Amplite® fluorogenic HRP substrates exploit the enzyme's peroxidase activity to generate bright fluorescent products through H₂O₂-dependent oxidation of non-fluorescent precursors. These fluorogenic substrates provide substantially higher analytical sensitivity than traditional colorimetric substrates such as TMB or ABTS when used with appropriate fluorescence detection instrumentation, supporting detection of low-abundance targets in microplate-based assays. Fluorimetric detection additionally provides superior specificity by minimizing spectral interference from colored samples and cellular autofluorescence.

ReadiUse™ and Amplite® colorimetric HRP substrates are pre-formulated, ready-to-use solutions optimized for standard ELISA and microplate assays with absorbance-based detection. TMB and ABTS remain widely used colorimetric substrates in research and industrial screening assays due to their well-characterized kinetics, established buffering conditions, and cost-effectiveness.

Chemiluminescent HRP substrates generate light through enzymatic H₂O₂-dependent oxidation of luminol derivatives, achieving femtogram-level protein detection sensitivity ideal for Western blotting and immunodetection applications. Enhanced luminol substrates such as Amplite® West ECL deliver extended signal duration and improved kinetics compared to first-generation luminol formulations, enabling multiple film exposures or prolonged digital imaging without signal decay.

Stayright™ Purple is an HRP chromogen that produces a stable purple precipitate with high contrast for immunohistochemical detection. It is a safer alternative to the standard brown DAB-based staining, which has been shown to be mutagenic and hazardous to laboratory workers and the environment. Stayright™ Purple is optimized for immunohistochemical detection in formalin-fixed paraffin-embedded (FFPE) tissue sections and multiplex applications where signal stability and color differentiation are critical.

In addition to substrates and activity assay kits, AAT Bioquest offers essential supporting reagents for development, optimization, and execution of HRP-based assays, including purified enzyme for protein conjugation, stabilized hydrogen peroxide substrate solutions, rapid reaction-stopping reagents, and signal amplification boosters. These components are critical for achieving reproducible assay performance and implementing advanced detection strategies.