Characterization of a highly purified membrane proteinase from bovine lens

A highly purified bovine lens membrane proteinase has been obtained. The purification was accomplished by solubilization of the proteinase from the membrane with 2% sodium deoxycholate followed by gel-filtration chromatography. The purified proteinase showed a major protein band having molecular weight of 17,000 on sodium dodecyl sulfate-polyacrylamide-gel electrophoresis (SDS-PAGE) and an active band on a non-denaturing acrylamide gel. The proteinase existed as a tetramer having a molecular weight of 68,000 as determined by gel-filtration chromatography. The proteinase had a pH optimum of 7.8 and was unstable above 40 degrees C. It lacked any requirement for metal ions for activity and was inhibited by all serine proteinase inhibitors tested. The proteinase hydrolysed mostly arginine amide and ester bonds. Based on its properties, the newly isolated membrane proteinase seems to be distinct from any mammalian lens proteinase isolated so far.