Table 1.

Modulation of Op18-tubulin binding affinities by phosphorylation and Glu-substitution of phosphorylation sites

	Kd1 ± SE (μM)	Kd2 ± SE (μM)	Free [tubulin] at Half saturation of Op18 (μM)
Op18-wt	7.2  ± 1.9	0.9  ± 0.3	2.5
Op18-tetraE	27  ± 7.2	2.7  ± 1.3	8.8
Op18-wt-16,63-PO4	61  ± 23	2.9  ± 1.8	13.4

Equilibrium dissociation constants at pH 7.5 were calculated according to a two-site positive co-operativity model and are based on the data shown in Figure 3, A and B. The free tubulin concentration at half saturation was estimated from curves fitted according to a two-site cooperativity model.