Binding proteins for methyl farnesoate in lobster tissues: detection by photoaffinity labeling

Methyl farnesoate (MF) is secreted by the mandibular organs of crustaceans, but its physiological role and biochemical distribution are only partially known. Characterization of specific MF binding proteins (MFBP) in homogenates of tissues of the American lobster, Homarus americanus, was achieved by photoaffinity labeling with tritium-labeled farnesyl diazomethyl ketone (3H-FDK). The tissues selected include epidermis, tail muscle, central nervous system, eyestalk, hemolymph, hepatopancreas, ovaries, testes, and Y-organ. Both high-speed pellets and supernatants were tested. Competing ligands employed to verify specificity of light-induced covalent modification included MF, methoprene, and unlabeled FDK. A 40-kDa band was labeled strongly in the hemolymph; the labeling was displaced in the presence of a 100-fold excess of unlabeled MF. Although many other tissues had proteins which labeled with 3H-FDK, none of these showed competition by MF. This MFBP is thus functionally analogous to the hemolymph JH-binding proteins of insects.