Identification and isolation of a mammalian protein which is antigenically and functionally related to the phospholipase A2 stimulatory peptide melittin.

Antibodies prepared against the phospholipase A2 stimulatory peptide melittin were used to identify and isolate a novel mammalian protein with similar functional and antigenic properties. The mammalian protein of Mr 28,000 was isolated from cell sonicates by high performance immunoaffinity chromatography and size exclusion chromatography. This stimulatory protein was stable for several months when frozen at -70 degrees C. The purified protein selectively stimulated phospholipase A2 when phosphatidylcholine was used as a substrate but had no effect on phospholipase A2 activity when phosphatidylethanolamine was used as a substrate. Furthermore, this protein had no effect on phospholipase C activity or on pancreatic or snake venom phospholipase A2. The stimulatory activity was unaffected by RNase or DNase treatment. However, boiling or trypsin digestion inactivated the phospholipase stimulatory activity. The mechanism of phospholipase A2 stimulation appeared to result from an increase in the apparent Vmax of the enzyme.