Phospholipase A2 from human synovial fluid: purification and structural homology to the placental enzyme.

Phospholipase A2 (PLA2) has been purified to homogeneity from synovial fluid of arthritis patients. The 3-step purification procedure included: a) dialysis against 5mM NH4-acetate, pH 5.5, in which PLA2 precipitated with euglobulins, followed by extraction with 0.4 M NaCl/0.05 M NH4-acetate, pH 5, b) chromatography on CM-cellulose, c) preparative gel electrophoresis in the presence of 0.1% Na-dodecyl sulfate and electroelution of the band containing the enzyme. Automated sequence analysis has indicated that the protein is pure, with the following NH2-terminal sequence: Asn-Leu-Val-Asn-Phe-His-Arg-Met-Ile-Lys-Leu-Thr-Thr-. A computer search revealed that all proteins with greater than 75% analogies in NH2-terminal sequences were PLA2's from various snake venoms. When PLA2 was purified from human placental membranes and analyzed, it was found to contain an identical sequence of 13 residues from the NH2-terminus. This and other characteristics suggest that the two human enzymes are closely related, if not identical.