Table 2. Biochemical properties of API paralogues from E. coli.
| E. coli API paralogue | |||
|---|---|---|---|
| Property | L-API* | G-API† | K-API |
| Km (A5P) | 0.61±0.06 mM | 1.2±0.1 mM | 0.57±0.04 mM |
| Km (Ru5P) | 0.35±0.08 mM | 0.64±0.08 mM | 0.30±0.03 mM |
| kcat (A5P to Ru5P) | 157±4 s−1 | 218±4 s−1 | 15±1 s−1 |
| kcat (Ru5P to A5P) | 255±16 s−1 | 242±11 s−1 | 19±2 s−1 |
| Keq (calc.)‡ | 0.47 (0.35) | 0.47 (0.48) | 0.48 (0.42) |
| Optimum pH | 8.4 | 8.25 | 7.75 |
| Specific for A5P/Ru5P§ | Yes | Yes | Yes |
| Zn2+/subunit∥ | 1.0±0.1 mol | 1.4±0.2 mol | 0.85±0.1 mol |
| Inhibition by 10 μM Zn2+¶ | Yes | Yes | Yes |
| Activation by 10 μM EDTA | Yes | Yes | Yes |
| Subunit mass** (calc.) | 35104 Da (35196 Da) | 33909 Da (34031 Da) | 35447 Da (35487 Da) |
| Native mass†† | 122±5 kDa (tetramer) | 133±4 kDa (tetramer) | 145±7 kDa (tetramer) |
* Data from [15].
† Data from [21].
‡ Measured by 31P NMR (calculated from Haldane relationship [Ru5P]/[A5P]).
§ See the Experimental section for tested substrates.
∥ Amount of Zn2+ per monomer as determined by high-resolution inductively coupled plasma-MS.
¶ Less than 5% activity remaining.
** Determined by electrospray ionization or MALDI-MS; calculated from protein sequence.
†† Determined by gel filtration.