Schematic representation of the two-headed kinetic model for the dynein stepping.37 Grey and black labels for states and transitions correspond to the grey and black heads, respectively. Each head can be in one of four biochemical states: nucleotide-free (Ø), ATP-bound (T), ADP·Pi-bound state (D·P), and ADP-bound state (D), and simultaneously in one of two conformational states: post-stroke (*) and pre-stroke. Shown is only a subset of states, which corresponds to the dominant pathways in the full multi-state network.