2 alpha-phosphohydantocidin: The in vivo adenylosuccinate synthetase inhibitor responsible for hydantocidin phytotoxicity

Hydantocidin is a phytotoxic natural product previously reported to inhibit purine biosynthesis at the site of adenylosuccinate synthetase. While hydantocidin does not inhibit this enzyme in vitro, Arabidopsis thaliana plants subjected to hydantocidin treatment were found to contain an inhibitor of adenylosuccinate synthetase. Alkaline phosphatase treatment of the plant extract significantly reduced inhibition, suggesting that the in vivo active molecule might be phosphorylated. 2 alpha-Phosphohydantocidin was synthesized and proved to be a potent inhibitor of rabbit muscle adenylosuccinate synthetase. This inhibition exhibited a time-dependent component not seen with hadacidin, a known competitive inhibitor with respect to aspartate at this site. The unidentified inhibitor produced in Arabidopsis eluted in the same fraction as 2 alpha-phosphohydantocidin following reversed-phase HPLC separation. Electrospray ionization mass spectrometry confirmed the presence of a molecule with a mass identical to that of 2 alpha-phosphohydantocidin in this same fraction. These data suggest that 2 alpha-phosphohydantocidin is the in vivo adenylosuccinate synthestase inhibitor responsible for hydantocidin phytotoxicity. (C) 1996 Academic Press