Kinesin: Hand-Over-Hand Stepping

Kinesin-1 walks on microtubules in discrete 8 nm steps, alternating its two heads. ATP hydrolysis provides the energy (~25 k_BT/step). The force-velocity curve shows stalling at ~7 pN.

[ATP] μM40
Load force (pN)0.0
Speed5
Kinesin moves by a "hand-over-hand" mechanism: the trailing head swings forward 16 nm past the leading head, landing 8 nm ahead (net displacement 8 nm). The step rate follows Michaelis-Menten kinetics: k = k_max·[ATP]/(K_m+[ATP]) with k_max≈100 s⁻¹, K_m≈90 μM. The stall force is ΔG_ATP/d ≈ 25 k_BT/8nm ≈ 13 pN (experiment: 5-8 pN due to inefficiency).