Many investigators prefer to use streptavidin rather than avidin as probes for biotin conjugated antibodies. Avidin (from egg white) is a glycoprotein with histone-like characteristics and a high isoelectric point(pI~10). Streptavidin lacks the glycoprotein constituent, has a much lower isoelectric point(pI~5), and is less likely to cause non-specific reactions. PROTOS IMMUNORESEARCH provides a variety of streptavidin conjugates. Streptavidin-peroxidase and streptavidin-alkaline phosphatase are available for ELISA, immunohistochemistry and immunoblotting. Streptavidin-fluorescein, -rhodamine, -Texas Red and -R.Phycoerythrin are suitable for use in immunofluorescence microscopy, flow cytometry and FACS analysis. Streptavidin-R.Phycoerythrin is particularly suited for assays involving bead-bound biotinylated analytes.