Ser202, Gln204, and Ser208. However, the same wild-type GFP could also crystallize as a monomer (32), isomorphous to the monomeric crystals formed by the S65T mutant (30). Even though GFP can hardly be more concentrated than in a crystal, the formation of dimers seems to be highly dependent on crystal growth conditions rather than an obligatory feature of GFP (33). The dissociation constant for the homodimer has been estimated as 100 µM (34a). By contrast, Renilla GFP is an obligate dimer, which is dissociated only under denaturating conditions (14).