RZ (Purity Value/Reinheitszahl) is the ratio of absorbances A403/A275 measured in deionized water at a concentration of 0.5-1.0 mg/ml. It is a measure of heme content, not enzymatic activity. Preparations with a high RZ value may still exhibit low enzymatic activity.One unit is defined as the amount of enzyme that produces 1.0 mg of purpurogallin from pyrogallol in 20 seconds at 20°C and pH 6.0.Horseradish peroxidase (HRP) is isolated from horseradish (Armoracia rusticana) and belongs to the ferriprotoporphyrin group of peroxidases. HRP is a single-chain polypeptide containing four disulfide bonds. It is a glycoprotein with a carbohydrate content of 18%. Depending on the specific isoenzyme, the carbohydrate composition includes galactose, arabinose, xylose, fucose, mannose, glucosamine, and galactosamine. Its molecular weight (~44 kDa) comprises the polypeptide chain (33,890 Da), hemin plus Ca²⁺ (~700 Da), and carbohydrates (~9,400 Da). There are at least seven HRP isoenzymes. The isoelectric points of horseradish peroxidase isoenzymes range from 3.0 to 9.0.
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