Table I. Binding and rate constants for the interaction of CP mutants and peptides with actin.
| Critical concentration experiment
|
Seeded assembly experiment
|
||||
|---|---|---|---|---|---|
| CP species | Actin | Kd | Kd | k+ 2 | k− 2 |
| nMa | nMb | μM−1s−1 | s−1 × 10−3 | ||
| Wild type | Muscle | 4 | 1.2 | 1.16 | 1.56 |
| Wild type | Yeast | 6.3 | 3.5 | 8.9 | 31.6 |
| Cap1Δ(239–268)/Cap2 | Muscle | 10,300 | 0.00022 | 2.33 | |
| Cap1/Cap2Δ(261–287) | Muscle | 25 | 7.8 | 2.09 | 16.3 |
| Cap1/Cap2Δ(261–287) | Yeast | 25 | 17 | 9.9 | 168 |
| Cap1/Cap2Δ(264–287) | Muscle | 25 | 8 | 2.1 | 17 |
| Cap1Δ(239–268)/Cap2Δ(264–287) | Muscle | 33,400 | 0.00037 | 12 | |
| Cap1 (W251A)/Cap2 | Muscle | 250 | 91 | 0.3 | 25.9 |
| Cap1 (R239A)/Cap2 | Muscle | 400 | 176 | 0.156 | 27.5 |
| Cap1 C-30 (peptide) | Muscle | 1,710 | 0.0021 | 3.6 | |
a
The value of Kd was determined from the [CP] that changes the critical concentration by 50%, as described in the Materials and methods.
b
The Kd was calculated from the k+2 (On) and k−2 (Off) rate constants by modeling the time course of polymerization with reaction 2 (see Materials and methods).