Studies on Cytochrome Reductase in Higher Plants

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Abstract
Cytochrome c reductase has been partially purified from an acetone powder of soybean leaves and evidence is presented that this or a similar enzyme is present in 15 other economically important higher plant species. Studies of the characteristics of the purest fraction showed that maximum activity was obtained at pH 8.5 and that DPNH was more effective as a reductant for the system than equivalent amounts of TPNH. An evaluation of the Michaelis constants for DPNH and cytochrome c indicated that the soybean enzyme has a much higher affinity for both these cofactors than the cytochrome reductase from pig heart. The soybean leaf enzyme was inhibited by Cu, Mn and Al ions and by p-chloro-mercuibenzoate, but was not appreciably influenced by such metal chelating agents as sodium azide, potassium cyanide, ethylenediaminetetraacetate, and sodium pyrophosphate. It has been demonstrated that soybean roots contain a cytochrome c reductase system that is active with both DPNH and TPNH and that a DPNH specific cytochrome reductase can be separated from crude extracts by centrifugation and (NH4)2SO4 precipitation. It was demonstrated also that the ratios of TPNH to DPNH activity of the leaf fractions failed to remain constant throughout the purification procedure, suggesting that more than one enzyme was involved.