Some aspects of rat platelet and serum phospholipase A2 activities

Rat platelet lysate contained appreciable phospholipase A2 activity. In agreement with literature data this enzymatic activity eluted in the void volume of a Sephadex G-100 column. When the void volume peak was chromatographed over a Matrex gel blue A column, part of the phospholipase A2 activity ran through, whereas the remainder was bound to the gel. The latter activity could be eluted with buffers containing a high salt concentration. In contrast, phospholipase A2 activity solubilized from rat platelet lysates by treatment with high salt eluted from Sephadex G-100 columns with an apparent molecular weight of 10-15 kDa. This solubilized enzyme completely bound to Matrex gel blue A and, in the presence of Ca2+ also to an alkylphosphocholine-AH Sepharose affinity column. No indications were obtained for the presence of inactive phospholipase A2 and activator proteins in rat platelet lysates as described by Etienne, J., Grüber, A. and Polonovski, J. ((1980) Biochim. Biophys. Acta 619, 693-698; (1982) Biochemie 64, 377-380). Phospholipase A2 activity, both the associated form in platelet lysate and the monomeric form as eluted from Sephadex G-100 was slightly inhibited by trifluoperazine but calmodulin exerted no stimulation. Likewise, phospholipase A2 activity from rat serum eluted in the void volume of a Sephadex G-100 column. Rather than indicating the presence of high molecular weight forms of the enzyme, this is apparently caused by association with lipids or other proteins, in that chromatography in the presence of high salt revealed a molecular weight similar to that found for solubilized platelet phospholipase A2 activity.