TABLE 2.
Concentration, activity, and predicted activity of proteases in human milk from mothers who delivered preterm infants (24–32 wk GA) during the first 7 wk of postnatal ages 2–47 d1
| Protease | ELISA-based concentration,2 ng/mL | Activity,3 ng/mL | Predicted activity (peptide abundance)4 |
| Carboxypeptidase B2 | 1574 ± 3 | 1900 ± 500 | 3.4 ± 0.4 × 1010 |
| Plasmin | 836 ± 128 | 146 ± 20 | 1.1 ± 0.1 × 1011 |
| Kallikrein | 700 ± 100 | 16,000 ± 2000 | 1.1 ± 0.1 × 1011 |
| Elastase | 382 ± 10 | 2.1 ± 0.3 | 6.5 ± 0.6 × 1010 |
| Thrombin | 25 ± 7 | 71 ± 13 | 1.1 ± 0.1 × 1011 |
| Cathepsin D | 0.8 ± 0.2 | ND | 5.3 ± 0.6 × 1010 |
| Cytosol aminopeptidase | 1.1 ± 0.1 | 1.0 ± 0.1 | 4.9 ± 0.5 × 1010 |
1
Values are overall means ± SEMs of the combined EGA and LGA preterm milks, n = 18. EGA, early gestational age; GA, gestational age; LGA, late gestational age; ND, not detected.
2
Concentration of the active enzyme and zymogen.
3
Determined with the use of fluorometric or spectrophotometric substrate assays and represents only the active enzyme.
4
Based on the total ion intensity ascribed to the protease (unitless).