Distribution of OM-hydrolyzing activity in lipoprotein fractions and LPDS separated from human serum
Human serum was fractionated into three lipoprotein fractions (VLDL including chylomicron, LDL, and HDL) and LPDS with a sequential ultracentrifugation method. The substrate concentration was 10 μM. The activity in the LPDS was tested in KPB and Tris-HCl buffer containing Ca2+ ions, because serum albumin previously showed higher activity for OM hydrolysis in KPB than in Tris-HCl buffer.
| Fraction | Incubation Buffer | Velocity | Protein Content | Distribution of OM-Hydrolyzing Activity |
|---|---|---|---|---|
| nmol · min−1 · mg protein−1 | mg protein/ml serum | nmol · min−1 · ml serum−1 (% distribution) | ||
| VLDL and chylomicron | Tris-HCl/Ca2+ | 13.9 | 0.174 | 2.42 (0.4) |
| LDL | Tris-HCl/Ca2+ | 12.6 | 0.323 | 4.07 (0.6) |
| HDL | Tris-HCl/Ca2+ | 277 | 2.15 | 596 (93.4) |
| LPDS | Tris-HCl/Ca2+ | 0.516 | 69.0 | 35.6 (5.6) |
| LPDS | KPB | 0.131 | 69.0 | 9.04 (N.C.) |
N.C., not calculated.