Action of paraquat and diquat on proteins and phospholipids

Abstract

The action of bipyridylium herbicides paraquat and diquat on some synthetic phospholipids and on papain and lysozyme was studied by differential scanning calorimetry. The phase transition parameters of phospholipids were only slightly affected by bipyridylium herbicides. Thus, the direct action of paraquat/diquat on phospholipids is of negligible importance. The phase transition parameters of papain and lysozyme were significantly modified by both compounds. Papain was affected to the same extent by diquat and paraquat. The phase transition temperature of lysozyme was more strongly increased by diquat than by paraquat. Our data suggest that both bipyridylium herbicides readily act on proteins, modifying their structure and function. As evidenced by charge transfer reversed-phase thin-layer chromatography, paraquat and diquat preferentially interact with dibasic and dicarboxylic amino acids like ornithine and glutamic acid.