Oxidation of reduced diphosphopyridine nucleotide by mitochondria from normal & crown-gall tissue cultures of tomato

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Abstract
Mitochondrial particles isolated from normal and crown-gall tomato tissue cultures were assayed spectrophotometrically for their DPNH oxidase, DPNH -cytochrome c reductase, cytochrome c oxidase, and diaphorase activities. Normal tissue particles always showed higher activities than crown-gall particles. There was no qualitative difference in their catalytic properties, and it was concluded that mitochondria from normal and crown-gall tissue cultures have virtually identical pathways for the transport of electrons from DPNH to oxygen. The effects of the osmotic properties of reaction mixtures on these enzymatic activities, especially the DPNH oxidase system, were studied. Without added cytochrome c, the maximum rate of DPNH oxidation was obtained in 0.2M sucrose, and in 0.2-0.8M mannitol. In the presence of cytochrome c, the oxidation rate was maintained at a maximum level at all concentrations used of sucrose or mannitol. DPNH-cytochrome c reductase activity, on the other hand, was accelerated in the absence of mannitol. The activity of cytochrome c oxidase was not affected appreciably in the hypotonic solution. Ascorbic acid had no effect on the rate of DPNH oxidation by the tissue culture mitochondria,.