Abstract
Leaf greening and senescence is one of drastic changes in plant life. Detailed mechanism of these events has not been revealed, however, proteasomes, an important regulator of life cycle, has some commitments to these dynamic conversions. Three types of proteasome-like activities were separated by DEAE-cellulose from green and senescent leaves of barley using a typical substrate of proteasomes, Suc-Leu-Leu-Val-Tyr-MCA. Two enzymes of these were activated by SDS at a concentration of 0.02% and 0.1% (w/v). These were inhibited by PSI, MG-115 and MG-132, specific inhibitors for proteasomes, except for the non-activated enzyme by SDS. The activity from 0.1% SDS increased dynamically accompanying greening, and dropped fairly along with leaf senescence. The activity from 0.02% SDS, which was a candidate for 20S proteasome, was stable throughout the leaf development. Its pH optimum was 8.5.
