TABLE 7.
Characteristics of soluble A1 ATPases from halophilic archaeaa
| Characteristic | Result or value for the following species:
|
|||
|---|---|---|---|---|
| H. saccharovorum | H. salinarum | H. volcanii | H. mediterranei | |
| Molecular mass (kDa) | 350 | 320 | 420b | ND |
| No. of subunit polypeptides | 4 | >2 | 4 | 4–7 |
| Sequenced genes | None | 2 (A, B) | A–E | None |
| Km [ATP] (mM) | 2.9 | 1.4 | 0.2 [Mn], 1.2 [Mg] | 5 |
| Ki [ADP] (μM) | 25–50 | 80 | 2.5 × 103 | ND |
| pH optimum | 8.5–10 | 5.8 | 9 (60°C) | 9 (60°C) |
| Azide inhibition | No/(yes)c | No | No | Yes |
| Nitrate inhibition | Yes | Yes | No (yes)e | Yes |
| Activating anion(s) | Cl−; SO3− | SO4− | NR | NR |
| NEM inhibition | Yes (A)d | Yes | Yes | Yes |
| NBD-Cl inhibition | Yes (B) | Yes | No | Yes |
| Inhibitory cation | ND | ND | Mn2+ | Mn2+ |
a
Data were compiled from references 111, 376, 493–495, 532, and 536; for comparison, detailed data on enzymatic properties of ATPases from Sulfolobus are contained in Table 6 and in reference 464. ND, not determined; NR, not reported.
b
Molecular mass calculated assuming an A3B3GDE stoichiometry.
c
Different in membrane-bound and solibilized states.
d
Indicates mainly labeled polypeptide.
e
Conflicting reports.