TABLE 2.
Effect of the reciprocal replacement of specific peptides containing eight amino acids of the α-glucosidases from T. thermophilus HB27 and GK24 on kinetic parameters determined with trehalose, isomaltose, and maltose as substratesa
| α-Glucosidase source | Trehalose
|
Isomaltose
|
Maltose
|
|||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Vmax | Km | kcat | kcat/Km | Vmax | Km | kcat | kcat/Km | Vmax | Km | kcat | kcat/Km | |
| HB27 | ||||||||||||
| Wild type | 333 ± 24 | 4.9 ± 1.4 | 343 ± 39 | 71 ± 11 | 250 ± 15 | 8.7 ± 1.8 | 257 ± 20 | 31 ± 5.9 | 21 ± 0.9 | 50 ± 3.3 | 22 ± 1.8 | 0.44 ± 0.02 |
| Mutantb | 46 ± 2.5 | 17 ± 0.8 | 47 ± 4.5 | 2.8 ± 0.4 | 286 ± 19 | 8.5 ± 0.7 | 295 ± 20 | 35 ± 2.5 | 1.9 ± 0.4 | 55 ± 6.3 | 2.0 ± 0.6 | 0.04 ± 0.02 |
| GK24 | ||||||||||||
| Wild type | 0 | 0 | 0 | 0 | 357 ± 42 | 5.2 ± 0.4 | 361 ± 44 | 68 ± 16 | 11 ± 0.6 | 69 ± 7.7 | 11 ± 0.9 | 0.17 ± 0.04 |
| Mutantc | 20 ± 0.1 | 6.9 ± 0.1 | 20 ± 1.3 | 2.9 ± 0.1 | 162 ± 8.0 | 4.1 ± 0.2 | 164 ± 12 | 39 ± 0.9 | 3.4 ± 0.1 | 72 ± 6.2 | 3.5 ± 0.1 | 0.05 ± 0.01 |
a
Vmax values expressed as μmol/min·mg protein, Km values expressed as mM, kcat values expressed as s−1, and kcat/Km values expressed as mM−1s−1. All values are means ± standard deviations.
b
HB27 α-glucosidase with the EPTAYHTL peptide of the GK24 enzyme (see Fig. 1).
c
GK24 α-glucosidase with the LGEHNLPP peptide of the HB27 enzyme (see Fig. 1).