Figure 7.

Relationship between susceptibility of rI_Na to be blocked by TTX and size of residue 7 of ddKIIIA[K7X]. Value of k_on for block of rI_Na with Na_V1.2 by TTX was estimated from observed rate constant of block (k_obs) of rI_Na at a single concentration of TTX and assuming k_off to be zero (see last column in Table 2). Data points are labeled as in Fig. 6. The plot suggests a general tendency that the smaller the rI_Na, the more TTX is impeded. Gray circles represent data for KIIIA and KIIIA[K7A] from (ref. 18), and KIIIA[K7D] (Tables 1 and 4); note, the data point for each peptide lies close to that of its disulfide-depleted counterpart.