Protein A is a highly stable surface receptor produced by Staphylococcus aureus, which is capable of binding the Fc portion of immunoglobulins, especially IgGs, from a large number of species (Boyle and Reis, 1987). Each protein A molecule can bind 2 molecules of IgG, allowing the formation of a precipitate (Sjoholm, 1975). Protein A Sepharose is prepared by covalently coupling Protein A to 6% cross-linked sepharose beads. The coupling technique is optimized to give a high binding capacity for IgG. The capacity of IgG binding could be up to 25mg of human IgG per ml of wet gel. High binding capacity (18-22mg/ml of gel); High flow rate; Low falling off of rProtein A. Applications: Purification of monoclonal and polyclonal antibodies. 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, goat, rat and s