Mechanism of Xanthine Oxidase Catalyzed Biotransformation of HMX Under Anaerobic Conditions

摘要

Enzyme catalyzed biotransformation of the energetic chemical octahydro-1,3,5,7-tetranitro- 1,3,5,7-tetrazocine (HMX) is not known. The present study describes a xanthine oxidase (XO) catalyzed biotransformation of HMX to provide insight into the biodegradation pathway of this energetic chemical. The rates of biotransformation under aerobic and anaerobic conditions were 1.6 0.2 and 10.5 0.9 nmol h 1 mg protein 1, respectively, indicating that anaerobic conditions favored the reaction. The biotransformation rate was about 6-fold higher using NADH as an electron-donor compared to xanthine. During the course of reaction, the products obtained were nitrite (NO ), methylenedinitramine (MDNA), 4-nitro-2,4-diazabutanal (NDAB), formaldehyde (HCHO), nitrous oxide (N2O), formic acid (HCOOH), and ammonium (NH+4 ). The product distribution gave carbon and nitrogen mass-balances of 91% and 88%, respectively. A comparative study with native-, deflavo-, and desulfo-XO and the site-specific inhibition studies showed that HMX biotransformation occurred at the FAD-site of XO. Nitrite stoichiometry revealed that an initial single N- denitration step was su cient for the spontaneous decomposition of HMX.