Binding‐Mechanism and Sensitivity in Gamete Chemotaxis of the Phaeophyte Cutleria multifida

Abstract

Female gametes of the marine brown alga C. multifida discharge mutifidene into the water to attract the swimming males. The physicochemical principle of interaction between semiochemical and membrane receptor site occurs in mutual but complementary induced dipoles. Halogenated derivatives of multifidene with intact overall structure and stereochemistry but altered electronic properties were synthesized and assayed as lures. A direct correlation occurred between increasing polarizability and biological activity, proving the proposed mechanism. The low threshold concentration of this communication system (4 .times. 109 molecules/ml), together with a detailed knowledge of the gamete''s architecture, swimming velocity and stimulus response time, indicates that very few, may be even single, molecules are able to trigger the sensomotoric chain. The rigidity of the natural signal molecule was recognized as an important element in inducing conformational fitting in the ligand/receptor complex.