Purification and properties of metal-chelating substance in chlorophyll degradation

Suzuki, T. and Inoue, M. and Shioi, Y. (2014) Purification and properties of metal-chelating substance in chlorophyll degradation. Journal of Tropical Plant Physiology, 6. pp. 35-49.

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Abstract

The early stage of degradation of chlorophylls includes the loss of phytol, magnesium and the oxidative cleavage (bleaching) of the tetrapyrrole macrocycle by the action of several enzymes or small molecular substance, so called metal-chelating substance (MCS). Pheophorbide formation due to the release of Mg from chlorophyllide in chlorophyll metabolism was studied using extracts of Chenopodium album and Raphanus sativus L. MCS was highly purified from C. album and some properties of MCS were investigated. Molecular weight of MCS was determined to be 452 by matrix-assisted laser desorption/ionization time-of-flight mass spectrometry. MCS gave a positive reaction with ninhydrin, confirming the presence of an amino group. Since MCS did not react with Ellman’s reagent and there was no absorption around 280 nm, it is clear that MCS has no sulfhydryl group including cysteine and aromatic amino acid. MCS chelated not only Mg2+, but also other divalent cations such as Zn2+ and Ni2+. Localization of MCS in radish seedlings showed that the activity of MCS was the highest in leaf and those of root and stem were 84% and 7% of the leaf, respectively. The results of present studies on the Mg-dechelating reaction are discussed in relation to the present understanding of metals in plant body. It is proposed that MCS is a novel chelator in plants and may play not merely Mg-dechelation from chlorophyllide a, but also other roles such as micronutrient transport.

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