Table 1. Comparison of activation constants for EPAC1 and EPAC2 obtained by in vitro biochemical Rap1 activation assays.
| EPAC1 | EPAC2 | |||
|---|---|---|---|---|
| AC50 [µM] | kmax | AC50 [µM] | kmax | |
| cAMP | 45 | 1.0 | 1.8 | 1.0 |
| 007 | 1.8 | 3.3 | 3.5 | 0.8 |
| S-220 | 13 | 0.3 | 0.1 | 7.7 |
| S-223 | 30 | 0.2 | 1.5 | 4.7 |
Half-maximal concentration for activation (AC50) describes the affinity of EPAC isoform for the cyclic nucleotide. Relative maximal activity (kmax) is the activity observed under saturating concentrations of the ligand and it is a measure of nucleotide's capability to shift the equilibrium towards the active state of EPAC.