Analytical Sciences

Characterization of Metal Binding Properties of Rhamnogalacturonan II from Plant Cell Walls by Size-Exclusion HPLC/ICP-MS

Toshiro MATSUNAGA* and Tadashi ISHII**

*National Agricultural Research Center for Kyushu Okinawa Region, Nishigoshi, Kumamoto 861-1192, Japan
**Forestry and Forest Products Research Institute, Tsukuba, Ibaraki 305-8687, Japan

The binding properties of metal ions to a pectic polysaccharide, rhamnogalacturonan II (RG-II), from plant cell walls were analyzed by size-exclusion HPLC/ICP-MS. The dimeric RG-II borate complex (dRG-II-B) from sugar beet and red wine contained 0.8 - 1.1 mol/mol of B, 0.8 - 1.1 mol/mol of Ca, 0.1 - 0.3 mol/mol of Sr, and 0.03 - 0.07 mol/mol of Ba. The treatment of dRG-II-B with Sr²⁺, Ba²⁺, Pb²⁺ or La³⁺ exchanged the originally present Ca, Sr and Ba. In contrast, monomeric RG-II (mRG-II), which contained ∼0.1 mol/mol of Ca, formed complexes with La³⁺, Eu³⁺, and Lu³⁺ added to the solution, but did not do so with Ca²⁺, Sr²⁺, Ba²⁺ and Pb²⁺. The HPLC/ICP-MS and HPLC/RI (refractive index detector) analysis of the partially hydrolyzed mRG-II that was treated with La³⁺ indicated that the side chains and backbone of mRG-II together form a lanthanoid binding site.

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