A Rapid Screening Method to Detect Specific Inhibitors of Pyruvate Orthophosphate Dikinase as Leads for C₄ Plant-Selective Herbicides

Abstract

Plants using the C4photosynthetic pathway are highly represented among the world’s worst weeds, with only 4 C4species being agriculturally productive (maize, sorghum, millet, and sugar cane). With the C4acid cycle operating as a biochemical appendage of C3photosynthesis, the additional enzymes involved in C4photosynthesis represent an attractive target for the development of weed-specific herbicides. The rate-limiting enzyme of this metabolic pathway is pyruvate orthophosphate dikinase (PPDK). PPDK, coupled with phosphoenolpyruvate carboxylase and nicotinamide adenine dinucleotide-malate dehydrogenase, was used to develop a microplate-based assay to detect inhibitors of enzymes of the C4acid cycle. The resulting assay had a Z′ factor of 0.61, making it a high-quality assay able to reliably identify active test samples. Organic extracts of 6679 marine macroscopic organisms were tested within the assay, and 343 were identified that inhibited the 3 enzyme-coupled reaction. A high confirmation rate was achieved, with 95% of these hit extracts proving active again upon retesting. Sequential addition of phosphoenolpyruvate and oxaloacetate to the assay facilitated identification of 83 extracts that specifically inhibited PPDK. ( Journal of Biomolecular Screening 2005:67-75)