Table 3.

Nucleotide exchange rates for muscle actin at low ionic strength in the presence of four different actin-binding proteins

Actin only	+HPRO1	+AtCAP1	+AtPRF4	+AtADF1a
0.005 ± 0.002 (17)	0.174 ± 0.012 (4)	0.32 ± 0.07 (4)	0.0074 ± 0.0005 (3)	0.00142 ± 0.00013 (3)

Nucleotide exchange rates are reported as the change in fluorescence (arbitrary units) per second ± SD (n), as determined by fitting experimental data to a single exponential function. The amount of actin-binding protein added corresponds to an amount that would give near saturation of monomers or >90% bound, based on the K_d values in Table 2 and our unpublished data. For human profilin (HPRO1), this amount corresponded to 3.8 μM; for AtCAP1, it was 6.03 μM; and for Arabidopsis profilin 4 (AtPRF4), it was 6.5 μM.

^a Because of limitations in the amount of protein that could be added to a reaction, AtADF1 was tested at 50% bound or 11.2 μM.