Figure 3. The interaction of the symmetry-related flavins and heme groups of the two@- chains in a tetrameric molecule. The cyano groups are roughly 3 A apart. The long axes of the isoalloxazine rings are not colinear; they are approximately parallel but displaced by about 1.4 A in the plane of the rings. donated by NAD (P) H to one flavin may also be transferred to the second flavin and subsequently to the second P-heme.