TABLE 3.
Biochemical characteristics of phospholipase mutants
| PC-PLC phenotypea | Mean in vitro enzymatic activity (nmol of substrate hydrolyzed/min/ml) ± SDb
|
Specificity (SM/PC) | |
|---|---|---|---|
| PC | SM | ||
| Wild type | 52 ± 18 (8) | 13 ± 3 (10) | 0.26 |
| D4E | 59 ± 27 (6) | 10 ± 3* (9) | 0.17 |
| H56Y | 92 ± 25** (8) | 35 ± 9*** (10) | 0.39 |
| D4E H56Y | 81 ± 29* (6) | 29 ± 6*** (9) | 0.36 |
| PLCBc | 570 ± 133*** (6) | 3 ± 3*** (9) | 0.004 |
a
All assays were performed in DP-L1553 (hypersecreting L. monocytogenes SLCC 5764, PI-PLC−) background (see also text).
b
L. monocytogenes culture supernatants were assayed for hydrolysis of isotope-labeled phospholipids in Triton X-100 mixed micelles (see Materials and Methods) at pH 7.2 and 37°C. Numbers of separate experiments are indicated in parentheses. Two-tailed P values of unpaired t tests are classified as follows: *, P < 0.05; **, P < 0.01; ***, P < 0.001 compared to values obtained with wild-type PC-PLC.