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 involvements 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 of them were activated by SDS at a concentration of 0.02% and 0.1% (w/v). The enzyme activated by 0.02% SDS was purified from green leaves of barley, and revealed as 20S proteasome. This enzyme showed an obvious SDS independent activity, though normal 20S proteasomes are inactive without SDS. We also purified 20S proteasome from senescent barley leaves. Comparison of these two 20S proteasomes is done in terms of subunit compositions and reaction mechanisms.
