In the first step of the reaction (TS1), the hydrogen atom from the C2 position is abstracted by a tyrosyl anion (Y363), which results in the formation of an enolate intermediate product E:I, as indicated by the shortening of the C2-C3 bond from 1.5Å in E:S to 1.38Å in E:I. At this point, the hydrogen bond network reorganizes, as Y363 and Y118 join the Y536 in H-bond stabilization of the negative charge at the 3-keto group of the steroid enolate. In the second step (TS2), a hydride anion from the 1C position is transferred to the N5 atom of FAD yielding reduced FADH -and 1-dehydro product (E:P). The stationary states of the pathway are presented in Figure .