Hydrogen Bonding of Cyanoacrylates with the D 1 Peptide

Abstract

Abstract Representatives of two structural types of cyanoacrylate PS II inhibitors have been studied in respect to their pI50 values and qualitative rate of binding with wild type and S 264 G mutant thylakoids isolated from Brassica napus. Both are potent inhibitors of photosynthetic electron transport and both show a large discrimination between wild type and mutant thylakoids under equilibrium conditions. However one, an N-methylanilino cyanoacrylate, has an initial rapid reaction with both wild type and mutant thylakoids, but continues to react slowly with the wild type species until equilibrium is reached, while the other, a benzylamino cyanoacry­ late, equilibrates rapidly with both species as does the classical PS II inhibitor, atrazine. These differences in kinetic behaviour have been interpreted in terms of different H-bond interactions with the serine-264 hydroxyl group. It is suggested that the slow binding reaction is due to the N -methylanilino compound interacting as an H-bond acceptor with the serine-264 hydroxyl hydrogen thus disrupting an intramolecular ser-264-his-252 H-bond within the D 1 peptide. Rapid equilibration on the other hand, has been attributed to the benzylamino derivative acting as an H-bond donor to the serine-264 hydroxyl oxygen and strengthening the 264 -252 H -bond by conjugation. It is proposed that atrazine and other classical PS II inhibitors act in this way and that this may explain their ability to inhibit trypsin degradation of the D 1 peptide, if the 264-252 intramolecular H-bond plays an important role in stabilizing the peptide conform ation. It is also speculated that photodegradation may be related to the ability of QB- to act as an H-bond acceptor and disrupt the 264-252 H-bond.