Protein extracts from the spicules of the sponge Clathrina and the ascidian Pyura pachydermatina have been reported (36, 37) to stabilize synthetic ACCs for up to 3 months. In this study, we demonstrate the capability of crustacean macromolecules to stabilize synthetic ACC. GAP 65 is a purified protein able to stabilize synthetic ACC that remains stable for up to 2 months. The manner by which GAP 65 stabilizes the ACC has yet to be elucidated.