title: Mg-dechelation activity in radish cotyledons with artificial and native substrates, Mg-chlorophyllin a and chlorophyllide a.
abstract: The Mg-dechelation activity in extracts from radish (Raphanus sativus L.) cotyledons was investigated using an artificial substrate, Mg-chlorophyllin a (Chlin) and the native substrate, chlorophyllide a (Chlide). In addition to a known a small molecular weight metal-chelating substance (MCS), Mg-releasing protein (MRP) was present when Chlin was used as the substrate. However, only MCS had Mg-dechelation activity with the native substrate. To examine the possibility of the dissociation of MRP into a protein moiety and a small molecular mass compound with an activity like MCS, extraction with low and high ionic strength buffers was carried out. No evidence was obtained that MCS is a moiety of MRP, however. Inhibitor studies showed that MCS and MRP had different susceptibilities to the inhibitors, especially to the chelators tiron and EDTA when Chlin was used as the substrate. Tiron had no effect on MRP, but it severely reduced MCS activity in both substrates. 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. These findings suggest that MRP and MCS are present independently, and MCS is postulated to be a substance that catalyzes the Mg-dechelation reaction in the breakdown pathway of Chl, although MCS was not induced during senescence. The properties of MRP and MCS in relation to the small molecular mass substance obtained from strawberry fruit are also discussed.
authors.affiliation: Department of Biological Science, Faculty of Science, Shizuoka University, Shizuoka 422-8529, Japan.
authors.forename: Toshiyuki
authors.initials: T
authors.lastname: Suzuki
authors.forename: Tadashi
authors.initials: T
authors.lastname: Kunieda
authors.forename: Fumiko
authors.initials: F
authors.lastname: Murai
authors.forename: Satoshi
authors.initials: S
authors.lastname: Morioka
authors.forename: Yuzo
authors.initials: Y
authors.lastname: Shioi
mesh_terms: D001383:Azetidinecarboxylic Acid / Q000031:analogs & derivatives / Q000378:metabolism; D002614:Chelating Agents / Q000494:pharmacology; D002735:Chlorophyllides / Q000378:metabolism*; D018548:Cotyledon / Q000187:drug effects / Q000201:enzymology*; D004492:Edetic Acid / Q000494:pharmacology; D004791:Enzyme Inhibitors / Q000494:pharmacology; D004798:Enzymes / Q000737:chemistry / Q000378:metabolism*; D008666:Metalloendopeptidases / Q000378:metabolism; D008970:Molecular Weight; D031224:Raphanus / Q000187:drug effects / Q000201:enzymology*; D013379:Substrate Specificity; D013997:Time Factors
chemical_list: D002614:Chelating Agents; D002735:Chlorophyllides; D004791:Enzyme Inhibitors; D004798:Enzymes; C421174:magnesium dechelatase; C034388:chlorophyllide a; D001383:Azetidinecarboxylic Acid; D004492:Edetic Acid; D008666:Metalloendopeptidases; C007020:chlorophyllin; C052863:mugineic acid