HRP consists of the basic isoenzyme having a molecular weight of 44 kDa.
Source
Root extracts of horseradish.
Storage Instructions
Lyophilized HRP although stable at room temperature for 3 weeks, should be stored desiccated below -18°C. Upon reconstitution HRP should be stored at 4°C between 2-7 days and for future use below -18°C.