TABLE 3.
Activities of the disulfide reductases studied as MB reductasesa
| Enzyme | Subunit Mr | KM of MB (μM) | kcat for MB (s−1) | kcat/KM (M−1 s−1) | IC50 for MB (μM) | KM for cogn. substrate (μM) | kcat for cogn. substrate (s−1) | NADPH auto-oxidase (s−1) |
|---|---|---|---|---|---|---|---|---|
| Human GR | 52.4 | 6.3 | 0.03 | 4,760 | 16.4 | 65 | 200 | 0.003 |
| Human GR C58A | 52.4 | 17 | 0.13 | 7,650 | NA | NA | NA | 0.005 |
| Human GR C63A | 52.4 | 56 | 0.62 | 11,100 | NA | NA | NA | 0.070 |
| Human GR C58A/C63A | 52.4 | 67 | 0.60 | 8,900 | NA | NA | NA | 0.065 |
| Human TrxR1 | 55.2 | 95 | 10.00 | 105,000 | 30 | 10 | 25 | 0.001 |
| Porcine LipDH | 55.0 | 28 | 3.40 | 121,000 | >1,000 | >1,000 | 290 | 0.220 |
| P. falciparum GR | 57.2 | 50 | 2.50 | 50,000 | 5.4 | 83 | 150 | 0.030 |
| P. falciparum TrxR | 60.3 | 68 | 6.30 | 88,200 | 59 | 2-10 | 50 | 0.006 |
| P. falciparum mtLipDH | 57.2 | 49 | 7.40 | 151,000 | >1,000 | >1,000 | 320 | ND |
a
GR was assayed in phosphate buffer at pH 6.9, TrxR was assayed at pH 7.4, and LipDH at pH 7.3. cogn., cognate; NA, for not applicable since the human GR mutants had no measurable activity when assayed with GSSG; ND, not determined.