Escherichia coliflavorubredoxin (FlRd) belongs to the family of flavodiiron proteins (FDPs), microbial enzymes that are expressed to scavenge nitric oxide (NO) under anaerobic conditions. To degrade NO, FlRd has to be reduced by NADH via the FAD-binding protein flavorubredoxin reduc-tase, thus the kinetics of electron transfer along this pathway was investi-gated by stopped-flow absorption spectroscopy.