Abstract
Chlorophyll degradation is ubiquitous phenomenon found in plants. The Mg-dechelating activity in extracts from radish (Raphanus sativus L.) cotyledons was investigated using an artificial substrate, Mg-chlorophyllin a and some activities were found. We designated them as MCS (metal-chelating substance) for low molecular mass compounds and MRP (Mg-releasing protein) for proteins. Inhibitor studies showed that MCS and MRP had different susceptibilities to the inhibitors when chlorophyllin was used as the substrate. Furthermore, the activity of MRP increased during senescence, indicating the induction of MRP, while the activity of MCS was almost unchanged. These results suggest different reaction mechanisms by independent compounds. Moreover, only MCS had Mg-dechelating activity from native substrate, chlorophyllide a, but MRP did not. These findings suggest that MCS is probably a substance that catalyzes the Mg-dechelating reaction in the native breakdown pathway of chlorophyll, although MCS was not induced during senescence.
