TABLE I.
Overview of the Kinetic Parameters of the PTB Binding Kinetics
| Toxin, experimental condition | k bind/s−1M−1 | k diss/s−1 | K m/nM |
|---|---|---|---|
| P. carib., renal enz., 50 NaCl | (0.90 ± 0.05) 105 | (9.0 ± 3) 10−4 | 10 ± 3 |
| P. toxica, renal enz., 50 NaCl | (0.80 ± 0.04) 105 | (13.0 ± 4) 10−4 | 16 ± 4 |
| P. tuberc., renal enz., 50 NaCl | (0.58 ± 0.01) 105 | (12.6 ± 5) 10−4 | 22 ± 5 |
| P. carib., salt gland, 50 NaCl | (1.87 ± 0.13) 105 | (19.5 ± 8) 10−4 | 10 ± 8 |
| P. carib., renal enz., 5 NaCl | ND | ND | 34.5 ± 6 |
| P. carib., renal enz., 50 NaCl | ND | ND | 31.8 ± 6 |
| P. carib., renal enz, 200 NaCl | ND | ND | 25.0 ± 4 |
| P. carib., renal enz, 0 NaCl, Pi | (0.208 ± 0.02) 105 | (29.6 ± 6) 10−4 | 142 ± 6 |
Three sources of PTX were used: from Palythoa caribaeorum (P. carib.), Palythoa toxica (P. toxica), and Palythoa tuberculosa (P. tuberc.). In the time-solved experiments, k bind and k diss were obtained from experiments and the equilibrium dissociation constant calculated as K m = k diss/k bind. The Na+ concentration dependence of PTX binding was performed as equilibrium titration experiments.