Table 1.
ATPase activities of wild-type and mutant HMMs
| HMM | MgATPase, nmol of
Pi per min per mg of protein
|
Actin-activated
MgATPase
|
||
|---|---|---|---|---|
| High salt | Low salt | Vmax, nmol of Pi per min per mg | Ka, M−1 × 10−3 | |
| Wild-type | ||||
| −kinase | 3.7 | 1.3 | 76 | 2.2 |
| +kinase | — | 3.2 | 637 | 10.4 |
| Mutant | ||||
| −kinase | 4.4 | 2.7 | 49 | 2.7 |
| +kinase | — | 5.8 | 65 | 1.9 |
Vmax is the maximum actin-activated ATPase activity of HMM and Ka is the apparent binding constant for HMM to actin, which is defined to be the reciprocal of the apparent Km from the double reciprocal plots (Fig. 4). To phosphorylate the regulatory light chain of HMM, myosin light chain kinase, calmodulin, and Ca2+ were added to the ATPase assay medium. —, Not measured.