Nitrate reduction by commercially available nitrate reductases: Bio-catalytic potentials and enzymatic activities in the presence of metals ions

Abstract

Commercially available nitrate reductases from corn, Aspergillus niger, and Escherichia coli have the potential to mitigate excess nitrate in soils and water sources. In this study, in vitro experiments were conducted to evaluate nitrate reduction by commercially available nitrate reductases from three major sources (plant, fungi and bacteria), their biocatalytic potentials and activities in the presence of varied concentrations of Cd²⁺, Cu²⁺, Ni²⁺, Co²⁺, Cr⁶⁺, Fe²⁺, Zn²⁺, and Pb²⁺. The results showed that the activity, V _max, and potential to reduce nitrate was in the order: corn > A. niger > E. coli. The kinetic constant (K _m) based on the various substrates used demonstrated that the binding affinity was generally highest for E. coli and lowest for A. niger. Based on the specificity constants obtained in this study, nitrate reductase from corn was the most efficient of all the enzymes assayed, yet that from E. coli showed the least. Nitrate reductase from corn and A. niger showed more variations with increase in metal ions concentrations compared to E. coli (with the exception of Cu²⁺). Information reported in this study will enable the assessment of the contributions and sources of nitrate reductases in mitigating environmental and health issues resulting from nitrate pollution.

Keywords:

• Nitrate reductases
• nitrate
• Michaelis-Menten constants
• corn
• A. niger
• E. coli

Acknowledgments

This work is a contribution of the Winfred Thomas Agricultural Research Station, Alabama A&M University, Normal, AL. Trade or manufacturers’ names mentioned are for information only and do not constitute endorsement, recommendation, or exclusion by Alabama A&M University. This research was supported in part by USDA-CSREES, Evans-Allen Grant # ALAX 011.