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Description

Substances with low molecular weights are generally not immunogenic and require the aid of carrier proteins to stimulate an immune response. Carrier proteins have relatively high molecular weights and carry many epitopes. An immune response to a hapten-carrier conjugate results in antibodies that are specific for both the hapten and the carrier. Hemocyanin is a high molecular weight respiratory metalloprotein found in the hemolymph of many mollusks and crustaceans. Molluscan hemocyanin is based on an approximately 400 kDa polypeptide subunit that is folded into a chain of multiple, immunologically distinct domains, each with a binuclear copper site. Keyhole Limpet Hemocyanin (KLH), the hemocyanin from the giant keyhole limpet, Megathura crenulata, is the most widely used carrier protein. It is an extremely large protein (6 - 7.5 million daltons) that can exist as a di-decamer, multi-decamers, or flexible tubules of varying length. It is easily dissociated into subunits and the dissociation-association reaction depends on protein concentration, ionic strength, and pH. At pH 6.5, KLH exists in a fully associated state without any evidence of dissociation products. In contrast, at pH 8.5 in borate saline the molecule is completely dissociated.