TABLE 5.
Activities of enzymes involved in the EMP pathway and the pathway leading to the biosynthesis of sugar nucleotides and EPS in cell extracts of the EPS-producing strain S. thermophilus LY03a
| Enzyme | Avg activity (nmol · mg of cell protein−1 · min−1) ± SD at indicated time point in:
|
|||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|
| 0.42 M glucose
|
0.28 M glucose + 0.14 M fructose
|
0.28 M glucose + 0.14 M galactose
|
0.28 M glucose + 0.07 M lactose
|
|||||||||
| 1 | 2 | 3 | 1 | 2 | 3 | 1 | 2 | 3 | 1 | 2 | 3 | |
| α-Phosphoglucomutase | 348 ± 55 | 597 ± 21 | 592 ± 10 | 507 ± 29 | 685 ± 9 | 700 ± 5 | 394 ± 7 | 549 ± 16 | 521 ± 15 | 568 ± 28 | 600 ± 3 | 530 ± 17 |
| 488 ± 7 | 542 ± 20 | 372 ± 12 | 525 ± 19 | 496 ± 9 | ||||||||
| β-Phosphoglucomutase | 0 ± 0 | 0 ± 0 | 0 ± 0 | 0 ± 0 | 0 ± 0 | 0 ± 0 | 0 ± 0 | 0 ± 0 | 0 ± 0 | 0 ± 0 | 0 ± 0 | 0 ± 0 |
| 0 ± 0 | 0 ± 0 | 0 ± 0 | 0 ± 0 | 0 ± 0 | ||||||||
| UDP-glucose pyrophosphorylase | 79 ± 14 | 122 ± 11 | 141 ± 5 | 119 ± 7 | 166 ± 4 | 170 ± 4 | 99 ± 2 | 125 ± 0 | 130 ± 4 | 216 ± 2 | 234 ± 16 | 217 ± 6 |
| 122 ± 11 | 128 ± 5 | 93 ± 3 | 141 ± 20 | 124 ± 2 | ||||||||
| UDP-galactose 4-epimerase | 172 ± 16 | 289 ± 32 | 238 ± 4 | 199 ± 13 | 287 ± 8 | 297 ± 12 | 166 ± 4 | 218 ± 0 | 227 ± 7 | 328 ± 3 | 344 ± 24 | 383 ± 20 |
| 253 ± 59 | 269 ± 13 | 183 ± 5 | 265 ± 35 | 236 ± 4 | ||||||||
| dTDP-glucose pyrophosphorylase | 1 ± 1 | 2 ± 1 | 0 ± 0 | 0 ± 0 | 1 ± 1 | 1 ± 1 | 0 ± 0 | 1 ± 1 | 0 ± 0 | 0 ± 0 | 0 ± 0 | 0 ± 0 |
| 1 ± 1 | 0 ± 0 | 0 ± 0 | 0 ± 0 | 0 ± 0 | ||||||||
| Dehydratase | 11 ± 2 | 16 ± 2 | 11 ± 2 | 8 ± 2 | 12 ± 1 | 8 ± 2 | 17 ± 1 | 25 ± 1 | 19 ± 1 | 6 ± 2 | 10 ± 2 | 3 ± 4 |
| 14 ± 1 | 9 ± 1 | 18 ± 1 | 22 ± 1 | 15 ± 3 | ||||||||
| Epimerase reductase | 0 ± 0 | 2 ± 1 | 0 ± 1 | 0 ± 0 | 1 ± 1 | 0 ± 0 | 1 ± 0 | 1 ± 0 | 1 ± 0 | 0 ± 0 | 1 ± 0 | 0 ± 0 |
| 0 ± 0 | 1 ± 0 | 0 ± 0 | 1 ± 1 | 0 ± 0 | ||||||||
| Phosphoglucose isomerase | 1,583 ± 296 | 1,807 ± 312 | 1,817 ± 245 | 1,839 ± 295 | 2,136 ± 365 | 1,910 ± 104 | 1,098 ± 81 | 1,275 ± 103 | 1,183 ± 95 | 1,934 ± 97 | 2,359 ± 91 | 2,041 ± 72 |
| 1,962 ± 284 | 2,080 ± 309 | 1,277 ± 254 | 1,258 ± 237 | 1,222 ± 51 | ||||||||
| 6-Phosphofructokinase | 1,928 ± 89 | 2,200 ± 85 | 2,224 ± 198 | 2,055 ± 48 | 2,381 ± 95 | 2,336 ± 127 | 1,344 ± 99 | 1,560 ± 127 | 1,501 ± 164 | 1,982 ± 27 | 2,457 ± 224 | 2,267 ± 121 |
| 2,392 ± 52 | 2,326 ± 90 | 1,307 ± 259 | 1,437 ± 120 | 1,495 ± 62 | ||||||||
| Fructose 1,6-bisphosphatase | 1 ± 1 | 5 ± 5 | 1 ± 1 | 0 ± 0 | 0 ± 0 | 0 ± 0 | 0 ± 0 | 0 ± 0 | 0 ± 0 | 9 ± 2 | 11 ± 1 | 6 ± 3 |
| 8 ± 3 | 0 ± 0 | 0 ± 0 | 0 ± 0 | 0 ± 0 | ||||||||
S. thermophilus LY03 was grown in batch cultures in MRS broth on glucose and combinations of glucose and lactose, glucose and galactose, and glucose and fructose as carbohydrate sources at 42°C and a constant pH of 6.2. Samples were taken at three time points of the fermentation course, representing the exponential growth phase (point 1), the end of the exponential growth phase (point 2), and the stationary phase (point 3). When two samples were taken in the exponential growth phase (point 1), two values are reported. Each value is always the average of at least three measurements.