Keyhole limpet hemocyanin

When oxygen is bound to hemocyanin, the molecule takes on a distinctive transparent, opalescent blue color, due to the Cu2+ state of the copper.

Because of its size and glycosylation, KLH protein cannot be reproduced synthetically; it is available only as a purified biological product from the keyhole limpet Megathura crenulata.

KLH is purified from the hemolymph of Megathura crenulata by a series of steps that typically includes ammonium sulfate precipitation and dialysis, and may involve chromatographic purification to obtain the highest purity.

Keyhole limpet hemocyanin (KLH) is used extensively as a carrier protein in the production of antibodies for research, biotechnology and therapeutic applications.

This method is the simplest to perform and the "random" orientation allows for antibody generation against all possible epitopes, but it generally results in some degree of polymerization, which decreases solubility making the conjugate more difficult to handle.

[4][5] These vaccines contain specific tumor-associated antigens conjugated to KLH to stimulate anti-tumor immune responses which can destroy tumor cells.

[2] In a 2006 report from the Marine Science Institute, University of California, Santa Barbara, scientists state that they are "very concerned about the emerging fishery" for Giant Keyhole Limpets and suggest the potential exists to "decimate their populations".