Apolipoprotein B exhibits phospholipase A₁ and phospholipase A₂ activities

Low density lipoproteins (LDL) as well as isolated apolipoprotein B (ApoB) have been shown to exhibit phospholipase A₂ (PLA₂) activity toward phospholipids containing an oxidized or short fatty acyl chain at position 2. Some of these studies employed the fluorescent analogue of phosphatidyl choline (PC), C₆-NBD-PC, containing NBD-caproic acid (C₆-NBD-FA) at position 2 as a substrate, representative of short fatty acyl chains. The release of NBD-caproic acid from position 2 is attributed to PLA₂-catalysed hydrolysis. However, this fatty acid can be released also by other enzymatic pathways. In the present study we examined, and ruled out, other enzymatic pathways which may be responsible for the hydrolysis of fatty acids from position 2 of phospholipids. On the other hand, we found that LDL as well as isolated ApoB hydrolyse C₆-NBD-FA from both carbon 1 and carbon 2 of these phospholipids, thus exhibiting independent and simultaneous activities of phospholipase A₁ and phospholipase A₂.