Abstract
Hydantocidin is a phytotoxic natural product previously reported to inhibit purine biosynthesis at the site of adenylosuccinate synthetase. While hydantocidin does not inhibit this enzymein vitro, Arabidopsis thalianaplants 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 thein vivoactive molecule might be phosphorylated. 2α-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 inArabidopsiseluted in the same fraction as 2α-phosphohydantocidin following reversed-phase HPLC separation. Electrospray ionization mass spectrometry confirmed the presence of a molecule with a mass identical to that of 2α-phosphohydantocidin in this same fraction. These data suggest that 2α-phosphohydantocidin is thein vivoadenylosuccinate synthestase inhibitor responsible for hydantocidin phytotoxicity.
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