Purification and Characterization of a DTT-sensitive Protease Associated with PS II Particles

A DTT-sensitive protease was purified by hydrophobic chromatography on butyl-Toyopearl 650 M and anion-exchange chromatography on DEAE-Sephadex A-50 from the 1 M NaCl extract of PS II particles. The results of SDS-PAGE and gel-filtration chromatography on Superose 12 Have showed that it is a monomeric protease with a MW of 37 000. The protease generated polypeptides of 13.2 kD, 12 kD and 10.5 kD fragments from 18 kD protein, and those of 23 kD, 22 kD and 20 kD fragments from 24 kD protein, respectively. The protease had maximum activity at pH 8.0, and showed to be sensitive to DTT and beta-Me but insensitive to the ionic strength of NaCl. Studies with protease inhibitors suggested that this enzyme is not a serine-protease.