Figure 5.

The affinity of ADP (K_AD) for acto-S1

The dissociation of acto-S1 was induced by ATP in the presence of ADP ranging from 0-1500 μM. The light scattering traces were fitted with single exponentials to determine the k_obs. Hyperbolic plots of the k_obs vs. ADP concentration were fitted with an equation derived from Scheme 1 (k_obs = K₁k₊₂([ATP]/(1 + [ADP]/K_AD)) to determine K_AD. Shown are the relative k_obs (k_rel) vs. ADP concentration plots for easier comparison. A) The fits yielded a value of 607 ± 44 μM for EMB-7d (empty squares) as compared to 587 ± 38 μM for EMB (filled squares). B) The fits yielded values of 409 ± 26 μM (open circles) for IFI and 239 ± 32 μM for IFI-7a (closed circles). The K_AD for EMB-7a/7d (C) and EMB-7d/7a (D) S1 isoforms were measured with the following alterations. The dissociation of acto-S1 was calculated in the presence of 0 – 400 μM ADP and the K_AD for EMB-7a/7d S1 was determined to be the ADP concentration at 50% inhibition. All preparations for EMB-7a/7d produced the sigmoidal-shaped curve observed here. The fits yielded values of 191 ± 59 μM for EMB-7a/7d and 220 ± 33 μM for EMB-7d/7a.