| Popis: |
This study deals with some kinetic properties of porcine pancreatic phospholipase A2 (PLA2) acting on neutral and anionic substrates. Short—chain diacylglycerosulfates possess a much higher affinity to the enzyme than the corresponding lecithins. At alkaline pH, micellar solutions of the negatively charged sulfates are hydrolyzed ten times faster than the zwitterionic lecithins. With both substrate classes, maximal enzymatic activity is always found in multimolecular aggregates containing several PLA2 molecules and a number of substrate monomers. The formation of these “high molecular weight” complexes, however, is different for lecithins and the anionic sulfates: with neutral phosphatidylcholine, the enzyme interacts with preformed micelles at substrate concentrations above the CMC. The zymogen has no affinity for these zwitterionic interfaces. The anionic lipids, however, induce enzyme aggregation already at substrate concentrations well below the CMC and the resulting complexes contain a premicellar aggregate of substrate monomers. In these rather unstable aggregates PLA2 displays very high enzymatic activity. Although the zymogen is also able to form similar high molecular weight complexes, this protein does not become activated. |
