Degradation of Metal—Nitrilotriacetate Complexes by Nitrilotriacetate Monooxygenase

摘要

Studies of metal-NTA complex degradation using NTA monooxygenase (NTA-Mo) can provide a mechanistic understanding of NTA degradation and lead to approachesto remediate recalcitrant metal— NTA complexes (e.g., NiNTA~-), NTA can exist in aqueous systems as various species depending upon the pH and types and concentrations of ions present (e.g., HNTA~(2-), CaNTA~-, MgNTA~-). An understanding of the aqueous speciation of NTA is necessary to determine the substrate range of NTA complexes degraded by NTA-Mo. The protonated form of NTA (HNTA~(2-)) and CaNTA~- were not degraded by NTA-Mo, while MgNTA~-, MnNTA~-, CoNTA~-, FeNTA~-, NiNTA~-, and ZnNTA~- were degraded with similar K_m's. This is surprising because these metal—NTA complexes have different rates of biodegradation by whole cells. This suggests that biodegradation of various metal—NTA complexes is limited by the rate of transport into the cell and that NTA-Mo may be useful for degrading metal-NTA complexes recalcitrant to degradation by whole cells. In mixed systems containing both substrate (MgNTA~-) and nonsubstrate (CaNTA~-), aqueous speciation modeling was able to provide the substrate concentration, which correlated well with the rate data (r~2 = 0.95). This demonstrates that aqueous speciation modeling can be used to predict the rate of NTA degradation by NTA-Mo for complex systems containing multiple species.