Fig. 1. Current model of the long-range PCET in E. coli RNR. R₄₁₁ is shown along with the redox active amino acid residues that are involved in this process (Y₁₂₂ ↔ [W₄₈?] ↔ Y₃₅₆ in β2 ↔ Y₇₃₁ ↔ Y₇₃₀ ↔ C₄₃₉ in α2). W₄₈, D₂₃₇ and E₃₅₀ are shown in grey, because currently there is no evidence for their role in this process.14 The locations of Y₃₅₆ and E₃₅₀ are unknown, as they are within the flexible C-terminal tail (35 amino acids) of β2. Red, blue and purple arrows represent electron transfer, proton transfer and collinear PCET pathways, respectively.