Protein G-gold complex: comparative evaluation with protein A-gold for high-resolution immunocytochemistry.

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Abstract
We combined the protein G-gold complex with several polyclonal and monoclonal antibodies for localization of various antigenic sites. The labelings were compared with those obtained using the protein A-gold complex. The results from either the immunodot experiment or immunoelectron microscopy have demonstrated that, for rabbit and guinea pig antibodies, both protein G-gold and protein A-gold complexes label several different specific antibodies with similar efficiency. However, with antibodies raised in goats or in mice, and particularly with mouse monoclonal antibodies, protein G-gold yielded intense and specific labeling, whereas protein A-gold yielded intense and specific labeling, whereas protein A-gold was very variable; it either gave weaker signals or failed to reveal any specific site or, as with one monoclonal, both protein G and protein A gave similar results. The higher affinity and versatility of protein G over protein A, established by the immunochemical approach, was confirmed by immunocytochemistry. Because of its enhanced reactivity with monoclonal antibodies and its broader affinity for polyclonal antibodies, protein G-gold complex appears to be a better and more versatile probe for high-resolution immunocytochemistry.