Enzymic properties of microsomes and mitochondria from silver beet

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Abstract
White petiole of silver beet (Beta vulgaris) was used to obtain cyto-plasmic components with minimal disruption of mitochondria or plastids. Particulate components were isolated by differential centrifuging of the tissue dispersion. Succinic-dehydrogenase DPNH-cytochrome c reductase and DPNH-diaphorase activities were determined on all fractions. The relative enzymic activities in the microsomal fraction were different from those in the mitochondrial fraction. The DPNH-cytochrome c reductase activity of the microsomes is not inhibited by antimycin A, while the similar activity of mitochondria is sensitive to very low concentrations of this antibiotic. The succinate-cytochrome c reductase activity of mitochodria is almost completely inhibited by low concentrations of antimycin A. This suggests that a factor, similar to the Slater factor, is concerned in the succinate-cytochrome c reductase system of plants. Fumaric-hydrogenase activity closely parallels that of succinic dehydro-genase, both in cytoplasmic localization and in lability. At least three different systems appear to contribute to the total DPNH-diaphorase activity of beet-petiole dispersions. Over 60% of the diaphorase activity occurs in the "soluble" supernatant fraction, and all the DPNH-cytochrome c reductase is associated with particulate material.