Table 1.
PfAct1 polymerization rate constants compared with smooth and skeletal muscle actin
| Actin | Assembly rate constant (subunits/µM·s) | Disassembly rate constant (subunits/s) | Critical concentration (µM) |
| PfAct1 + JAS* | 4.9 | 0.03 | 0.005 |
| PfAct1† | 3.8 ± 1.0 | 14.8 ± 0.4 | 4.1 ± 1.0 |
| PfAct1 + BeFx‡ | 2.6 ± 0.7 | 11.2 ± 3.7 | 4.2 ± 0.3 |
| PfAct1-ADP§ | 0.18 | 9.8 | 55 |
| PfAct1 (human D-loop)¶ | 9.2 ± 3.1 | 7.4 ± 0.5 | 0.86 ± 0.33 |
| Smooth muscle actin (ACTA2)# | 15.9 ± 3.4 | 0.7 ± 0.6 | 0.05 ± 0.04 |
| Skeletal muscle actin (ACTA1)‖ | 7.4 ± 0.5 | 0.8 ± 0.8 | 0.13 ± 0.17 |
| Skeletal muscle actin (ACTA1) visualized with actin-chromobody** | 8.2 | 2.1 | 0.25 |
Rate constants were obtained from the plot of assembly rate versus actin concentration, with the slope defining the assembly rate constant, the y-intercept the disassembly rate constant, and the x-intercept the critical concentration. Error bars ± SD. Rates of PfAct1 assembly were obtained during the first 6 min of polymerization for actin-ATP, or the first 2 to 3 min for actin-ADP. Filaments that grew at the barbed end and showed no shrinkage at the pointed end were analyzed. PfAct1 polymerization buffer: 10 mM imidazole, pH 7.5, 50 mM KCl, 2 mM MgCl2, 1 mM EGTA, 2.5 mM MgATP,10 mM DTT, 0.25% methylcellulose, 0.13 mg/mL glucose oxidase, 50 μg/mL catalase, and 3 mg/mL glucose. Data with PfACt1 were obtained at 37 °C; ACTA1 data are at 25 °C.
Data from 1 experiment with 1 PfAct1 preparation.
Data from 4 experiments with 3 PfAct1 preparations.
Data from 2 experiments with 2 PfAct1 preparations.
Bound nucleotide in PfAct1 was converted to ADP prior to polymerization (Materials and Methods). Fit to data from 2 independent experiments combined, 1 PfAct1 preparation.
Data from 2 experiments with 1 PfAct1 preparation.
Data from ref. 23.
Data from ref. 17, 25 °C.
Data obtained here using actin-chromobody, at 25 °C for comparison with published values. 1 experiment, 1 skeletal actin preparation (SI Appendix, Fig. S1).