TABLE 3.
Specific enzymatic hydrolysis of 2-3′ and 2-6′ sialyl lactose by sialidase preparations from P. multocida isolates and clones
| Sialidase sourcea | Sialic acid release from sialyl lactoseb
|
Ratio of 2-3′ to 2-6′ activity | |
|---|---|---|---|
| 2-3′ linked | 2-6′ linked | ||
| NanH (pNEU101) | 2.5 | 0.1 | 25.0 |
| NanB (pAH502) | 1.8 | 6.4 | 0.3 |
| P. multocida 86-1913 | 1.3 | 0.2 | 6.5 |
| P. multocida X-73 | 1.5 | 2.4 | 0.6 |
| P. multocida P1059 | 1.4 | 0.8 | 1.8 |
| P. multocida P1059 NanH mutant | 0.9 | 1.2 | 0.8 |
a
Sonicated bacterial cell lysates were used as crude sialidase preparations for the enzyme assays. Sialidase-encoding constructs pNeu101 and pAH502 were expressed in E. coli DH5α. E. coli cells harboring only vector did not produce any detectable sialidase activity.
b
Results are expressed as micromoles of sialic acid (Neu5Ac) released per unit of enzyme per minute. A total of 2 × 10−3 U of sialidase was incubated with 1 mM substrate for 10 min. One unit of sialidase activity was defined as the amount that releases 1 μmol of 4-methylumbelliferone from 4MU-Neu5Ac per min.