Synthesis and Use of Radiolabelled Cyanoacrylate Probes of the Photosystem II Herbicide Binding Site

Abstract

Abstract Cyanoacrylates are potent inhibitors of photosynthetic electron transport (PET) and are potentially useful probes of the photosystem II herbicide binding site. A series of cyanoacrylates was synthesized and the Hill inhibition activities evaluated in order to select compounds suita­ble for radioactive synthesis. A cyanoacrylate, 2-(2-nitrophenoxy)ethyl 3-benzylamino-2-cyano-2-pentenoate, was found to displace diuron from the photosystem II herbicide binding site. For this compound the dissociation constant of the inhibitor/binding site complex was found to be 2 × 10-8 M with an active site concentration of 2 nmol/mg chlorophyll. In a similar system the corresponding figures for diuron were 1.2 × 10-8 m and 1.3 nmol/mg chlorophyll. Photoaffinity labelling of 1% II thylakoid proteins with 2-(2-azidophenoxy)ethyl 3-[7-14C]-benzylamino-2-cyano-2-pentenoate showed weak binding in the 32 and 28 kD mass regions, consistent with binding to the D, peptide.