Abstract: The purpose of the work is to purify the isocitrate dehydrogenase（IDH）in mycorrhizal tissue of Suillus luteus-Pinus sylvestris var. mongolica, root tissue of P. sylvestris var. mongolica and cultured fungal mycelia of S. luteus, and identify their enzymatic characterizations. The IDHs of 3 sources were purified by ammonium sulfate precipitation and glucan gel chromatography and tested by SDS-PAGE electrophoresis, and enzymatic characterizations were studied. The K_m for NADP⁺ of mycorrhiza, root and cultured fungal mycelia were 10.7 μmol/L, 11.4 μmol/L and 22.1 μmol/L, respectively;the K_m for isocitrate were 71.7 μmol/L, 79.3 μmol/L and 87.8 μmol/L, respectively. The optimal pH of mycorrhiza, root and cultured fungal mycelia were 8.2, 8.0 and 7.5 respectively;they were all slightly in alkaline. The optimal temperatures of the IDHs were 45℃ for mycorrhiza and root, and 42℃ for the fungus. The activities of 3 IDHs relied on the binding of divalent metal ions, the maximum activities of IDHs were observed when assayed with Mn²⁺ or Mg²⁺ as metal cofactor;however, Ca²⁺, Co²⁺, Cu²⁺ and Zn²⁺ dramatically inhibited the activity of IDHs. Conclusively, protein content and enzyme activity of mycorrhizal IDH have been increased.

Key words: Pinus sylvestris var. mongolica, mycorrhiza, isocitrate dehydrogenase, enzymatic characterization