Figure 1.

Proposed radical initiation pathway in E. coli class Ia RNR. Radical transfer occurs by orthogonal PCET within β2, where long-distance ET within the pathway is coupled to short-distance off-pathway PT, and by collinear PCET (or hydrogen atom transfer) within α2. Note that the position of Y₃₅₆ is structurally unknown.¹⁹