Chemo-chemical molecular machine. A scheme of two coupled free energy-donating R1 ⇔ P1 and free energy-accepting R2 ⇔ P2 enzymatic reactions involving the intramolecular conformational dynamics of the enzyme macromolecule. The multitude of conformational transitions within the complex M is represented by the shaded box. Both coupled reactions are assumed to be gated by certain conformational substates distinguished here as the black dots. The transitions between gates are characterized by the external transition times τ1 and τ2.