[Biochemical and immunological properties of EEP 32 kd protein]

EDTA-extractable protein (EEP) is a major extrinsic protein of lens membrane. EEP is composed of two major polypeptides on SDS-PAGE with apparent molecular weights of 32 kilodaltons (kd) and 34 kd. Recently it has been reported that the 34 kd protein of the EEP cross-reacted with the antibody prepared against lipocortin, an inhibitor of phospholipase A2. We have purified and characterized the 32 kd protein of the EEP (EEP 32). Crude EEP of bovine lens was applied to a Q-Sepharose column and eluted with a linear gradient system composed of 0-0.7 M NaCl. The EEP 32 was discreted at salt concentrations of approximately 0.1-0.25 M (EEP 32-A) and 0.35-0.4 M (EEP 32-B). Both EEP 32-A and EEP 32-B interact with phospholipid and F-actin in a Ca2+-dependent manner as lipocortin. Furthermore, the EEP 32-A, a major component of the EEP 32 purified by hydroxyapatite chromatography and gel filtration, inhibited phospholipase A2 activity more than lipocortin. On Western blot analysis, the 32 kd lipocortin-like protein of human placenta showed cross-reactivity to EEP 32-B, but not EEP 32-A. These results suggest that EEP 32 contains two lipocortin-like proteins differing in antigenicity and isoelectric points.