The Effect of Temperature on the Energy of Activation of Spinach Ferredoxin-NADP^+ Oxidoreductase

概要

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A non-linear Arrhenius plot of diaphorase activity of the membrane-bound ferredoxin-NADP^+ oxidoreductase of thylakoids, showed a break at 25-30℃, whereas a straight-line was obtained for the soluble reductase. The E_a values of the thylakoid-bound enzyme was 4-7 and 15-18 kJ/mol above and below the transition temperature, respectively. In contrast, the E_a obtained for the soluble enzyme was in the range 25-30 kJ/mol. An Arrhenius plot with similar transition to that of thylakoids, but with higher E_a values, was obtained when the reductase was isolated as a complex closely associated with the 17.5 kDa-intrinsic polypeptide. The differences in ΔH* and in ΔS* values below and above the transition temperature for thylakoids and the complex were almost the same suggesting that lipids were not important for the transition. Comparing the ΔH* and ΔS* values for the diaphorase activity of soluble and membrane-bound enzyme suggest that the conformation of the latter is more favorable for catalysis.
日本植物生理学会の論文