Other Secondary Probes
Protein A is the component of the cytoderm of staphylococcus aureus. It can bind Fc fragments of a majority of immunoglobulin. Protein G is an immunoglobulin-binding protein expressed in group C and G Streptococcal bacteria much like Protein A but with differing specificities. Both proteins are regarded as broad spectrum secondary antibodies and also are used in antibody purification.Avidin is a 68 kD protein extracted from egg white. Streptavidin is a 47 kD protein extracted from streptomyces. Both avidin and streptavidin have very high affinity to biotin molecule, one million times higher than the common affinity between antigen and antibody. Thus avidin and streptavidin are regarded as secondary antibodies when used with biotin conjugated primary antibodies.
