Table 2.

Rate of detachment of kinesin from microtubules

Nucleotide condition	One-headed rate, s−1	Two-headed rate, s−1
1 mM ATP	2.9 ± 0.4	48 ± 2
1 mM ADP	3.7 ± 0.4	1.01 ± 0.28
1 mM ADP + 10 mM Pi	3.8 ± 0.6	1.67 ± 0.50
No nucleotide	0.019 ± 0.007	0.0009 ± 0.0002
1 mM AMP-PNP	0.009 ± 0.002	0.0010 ± 0.0004

All rates were measured for kinesin bound to beads (one motor/bead). In the case of two-headed kinesin in ATP, the detachment rate was calculated by dividing the bead velocity [770 nm/s (13)] by the step size of 16.2 nm per head; the observed rate for release of these beads from microtubules were 0.66 ± 0.16 s⁻¹. 1 mM ADP samples contain ≈2 μM contaminating ATP, and no nucleotide contains 100 nM ADP and ≈1 nM ATP.