Keyhole Limpet Hemocyanin (KLH)

Keyhole limpet hemocyanin (KLH) is a large, multisubunit, oxygen-carrying, metalloprotein found in the hemolymph of the giant keyhole limpet, Megathura crenulata, that lives off the coast of California from Monterey Bay to Isla Asuncion off Baja California. Keyhole limpet hemocyanin is an extremely large, heterogeneous glycosylated protein consisting of subunits with a molecular weight of 350,000 and 390,000 in aggregates with molecular weights of 4,500,000-13,000,000. When oxygen is bound to hemocyanin, the molecule takes on a distinctive transparent, opalescent blue color. The KLH protein is potently immunogenic yet safe in humans and is therefore highly prized as a vaccine carrier protein. The large and highly glycosylated KLH protein cannot be reproduced synthetically. It is available only as a purified biological product from the Keyhole Limpet Megathura crenulata.