Degradation of metal-nitrilotriacetate complexes by nitrilotriacetate monooxygenase

Studies of metal-NTA complex degradation using NTA monooxygenase (NTA-Mo) can provide a mechanistic understanding of NTA degradation and lead to approaches to 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 MTA-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.