Table 2. Kinetic parameters of human wild-type and mutant DGUOK enzymes with the phosphate acceptors.
Samples containing 5 μg of mitochondrial protein were assayed under standard conditions (see the Subjects and methods section). The phosphate acceptor concentrations were varied from 0.3 to 50 μM and from 0.6 to 50 μM for dG and dA respectively. The ATP/MgCl2 concentration was fixed at 5 mM/6 mM. The three controls were within the age range of patients. For the patients, the values are from three different experiments. The apparent Km and Vmax values were calculated using the Hanes equation (s/v versus s). Km is given in μM and Vmax is given in picomoles of dG or dA phosphorylated per hour per milligram of protein. Also shown is the percentage of the mean control value.
| dG | dA | |||||
|---|---|---|---|---|---|---|
| Km,app | Vmax/Km,app | Hill constant | Km,app | Vmax/Km,app | Hill constant | |
| Controls (n=3) | ||||||
| Mean | 1.8 | 437 | 0.53 | 6.8 | 337 | 0.75 |
| Range | (1.5–2.6) | (383–585) | (0.45–0.65) | (5.3–7.6) | (296–443) | (0.70–0.80) |
| Carriers | ||||||
| Mother (N46S) | 2.8 | 181 (41%) | 0.46 | 5.3 | 262 (78%) | 0.79 |
| Father (L266R) | 2.3 | 140 (32%) | 0.50 | 3.5 | 252 (75%) | 0.81 |
| Brother (N46S) | 1.9 | 204 (47%) | 0.59 | 4.1 | 233 (69%) | 0.74 |
| Mother (c.763_766dupGATT) | 1.6 | 222 (51%) | 0.59 | 4.8 | 184 (55%) | 0.75 |
| Patients | ||||||
| Patient 1 (N46S, L266R) | 3.4 | 39 (9%) | 0.61 | 2.6 | 83 (25%) | 0.68 |
| Patient 2 (c.142+1G>A, c.591G>A) | No kinetics | No kinetics | ||||
| Patient 3 (c.763_766dupGATT) | No kinetics | No kinetics | ||||