Figure 1.

Steady-state kinetics of Cin8 motors reveals typical microtubule-stimulated ATPase. A, ATP-stimulated activity for Cin8 at low (closed circles) and high (open circles) ionic strength (IS). Final concentrations are 0.1 μm Cin8-His, 2 μm microtubules, and 5–1000 μm ATP. Data were fit to Equation 1. Low, k_cat = 0.54 ± 0.01 s⁻¹ site⁻¹ and K_{m, ATP} = 29 ± 2 μm. High, k_cat = 0.42 ± 0.01 s⁻¹ site⁻¹ and K_{m, ATP} = 12 ± 1 μm. B, microtubule-stimulated ATPase activity for Cin8 at low ionic strength. Final concentrations are 0.01 μm Cin8-His, 0–2 μm microtubules, and 1 mm ATP. Data were fit to Equation 2 to yield k_cat at 0.38 ± 0.01 s⁻¹ site⁻¹ and K_{0.5, MT} = 0.08 ± 0.02 μm. C, microtubule-stimulated activity for Cin8 at high ionic strength. Final concentrations are 0.2 μm Cin8, 0–30 μm microtubules, and 1 mm ATP. Data were fit to Equation 2 to yield k_cat at 0.68 ± 0.02 s⁻¹ site⁻¹ and K_{0.5, MT} = 1.8 ± 0.2 μm. k_basal was 0.01 ± 0.02 s⁻¹ site⁻¹ at low and 0.02 ± 0.02 s⁻¹ site⁻¹ at high ionic strength.