Activation of the Class Ib Ribonucleotide Reductase by a Flavodoxin Reductase in <i>Bacillus cereus</i> Marie Lofstad Ingvild Gudim Marta Hammerstad Åsmund Kjendseth Røhr Hans-Petter Hersleth 10.1021/acs.biochem.6b00699.s001 https://acs.figshare.com/articles/journal_contribution/Activation_of_the_Class_Ib_Ribonucleotide_Reductase_by_a_Flavodoxin_Reductase_in_i_Bacillus_cereus_i_/3793542 To reduce ribonucleotides to deoxyribonucleotides, the manganese-bound form of class Ib ribonucleotide reductase (RNR) must be activated via a pathway that involves redox protein(s). The reduced flavoprotein NrdI is an important protein in this pathway, as it reduces dioxygen to superoxide. Superoxide then reacts with the RNR Mn<sup>II</sup><sub>2</sub> site to generate a tyrosyl radical that is required for catalysis. A native NrdI reductase has not yet been identified. We herein demonstrate through kinetic and spectroscopic studies that an endogenous flavodoxin reductase can function as the NrdI reductase in <i>Bacillus cereus</i>. When the flavodoxin reductase reduces NrdI, tyrosyl radical formation in RNR is promoted under aerobic conditions, significantly increasing the radical yield. Thus, a missing piece of the class Ib RNR NrdI redox pathway has finally been identified. 2016-08-25 00:00:00 flavodoxin reductase tyrosyl protein NrdI reductase Bacillus cereus class Ib RNR NrdI redox pathway RNR Mn II 2 site class Ib ribonucleotide reductase Class Ib Ribonucleotide Reductase