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Plant and Cell Physiology, 1986, Vol. 27, No. 6 1141-1145
© 1986

Article

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

Aurelio Serrano1, Fernando Soncini and Rubén H. Vallejos

Cenlro de Estudios Fotosinleticos y Bioquímicos, CEFOBI {Consejo Nacional de livestigaciones Cientificas y Teécnicas, Fundación M. Lillo, Univ. Nac. de Rosario) Suipacha 531, 2000 Rosario, Argentina

A non-linear Arrhenius plot of diaphorase activity of the membrane-bound ferredoxin-NADP+ oxidoreductase of thylakoids, showed a break at 25–30°C, whereas a straight-line was obtained for the soluble reductase. The Ea values of the thylakoid-bound enzyme was 4–7 and 15–18 kj/mol above and below the transition temperature, respectively. In contrast, the Ea 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 Ea values, was obtained when the reductase was isolated as a complex closely associated with the 17.5 kDa-intrinsic polypeptide.

The differences in {Delta}H* and in {Delta}S* 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 {Delta}H* and {Delta}S* values for the diaphorase activity of soluble and membrane-bound enzyme suggest that the conformation of the latter is more favorable for catalysis.

1Present address: Depto. de Bioquímica, Fac. de Biologia y C.S.I.C., Univ. de Sevilla, Apdo. 1095, 41080-Sevilla, Spain

(Received May 1, 1986; Accepted June 18, 1986)
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