Characterization and physical properties of the major form of phospholipase A2 from cobra venom (Naja naja naja) that has a molecular weight of 11,000.

The major form of phospholipase A2 from cobra venom (Naja naja naja) was prepared in 30% yield and was homogeneous on polyacrylamide gel electrophoresis with and without sodium dodecyl sulfate and on Sephadex G-100 chromatography. The monomer molecular weight is about 11,000 according to sodium dodecyl sulfate-polyacrylamide gel electrophoresis. Ultracentrifugation and molecular sieve techniques were employed to confirm the molecular weight and to demonstrate a concentration-dependent aggregation of the enzyme. It was found that at concentrations below about 0.05 mg ml(-1), the enzyme exists predominantly in the monomeric form; kinetic studies are usually conducted in much more dilute solutions (0.2 mug ml(-1)). The amino acid composition of the enzyme is reported. Of special interest is the presence of five to six disulfide bonds, 1 tryptophan residue, and 1 histidine residue. It is stable at high temperatures and is unusually resistant to denaturing agents. The isoelectric point was found to be 4.95. The findings that the protein is unusually resistant to denaturing agents and that it undergoes a concentration-dependent aggregation help to explain some of the previous reports in the literature on the apparent multiple forms of the cobra enzyme and their separation.