Purified protein A is a highly stable cell surface receptor produced by several strains of Staphylococcus aureus. With a molecular weight of 35,000 Da, it is made up of a single polypeptide chain containing five Ig-binding regions. Purified protein A is ideal for purification of polyclonal or monoclonal IgG antibodies. Purified protein A binds to most human and mouse IgG subclasses (e.g. human IgG1, IgG2, IgG4 mouse IgG1, IgG2a, IgG2b, IgG3). It also binds to total IgG from cow, guinea pig, hamster, horse, pig, and rabbit. Protein A has little affinity to chicken IgY.