Abstract

NM441 is a prodrug of the new quinolone carboxylic acid antibacterial agent NM394. A rat serum enzyme (NM441-hydrolase) that catalyzes the hydrolysis of NM441 to NM394 was purified by ultracentrifugation, heparin-Sepharose column chromatography, and HPLC with a Mono Q anion exchange column. The enzyme showed a single protein band after sodium dodecyl sulfate-polyacrylamide gel electrophoresis. Its molecular mass was estimated as 46 kDa. The amino-terminal sequence and two internal amino acid sequences of the NM441-hydrolase resemble those of mouse, rabbit, and human serum paraoxonases. Moreover, its enzymatic characteristics (optimum pH, calcium requirement, and molecular mass) were similar to those of the paraoxonases. These findings identify the NM441-hydrolase as rat serum paraoxonase. To determine whether the paraoxonase catalyzes the hydrolysis of NM441 to NM394 in human serum, we investigated whether the paraoxonase and NM441-hydrolase activities were correlated. There was a positive correlation (r = 0.653, p < 0.005) found in the sera of 67 healthy volunteers, indicating that paraoxonase is responsible for the conversion of NM441 to NM394 in humans. Human paraoxonase shows polymorphism. There was a 9-fold variation in paraoxonase activity but only a 2-fold variation in NM441-hydrolase activity. These findings show that paraoxonase polymorphism does not cause marked interindividual variation in NM441-hydrolase activity and is substrate dependent.