Effects of salts on DPNH oxidase activity & structure of sweet potato mitochondria

Abstract

The fact that inorganic salts can stimulate the oxygen consumption of many plant tissues has raised the possibility that the salts may exert a direct influence on the activity of the respiratory chain. Work in several laboratories (1, 17) has shown that the cytochrome c oxidase activity of isolated mitochondria can be stimulated by relatively high salt concentrations, but the physiological significance of this effect is not clear. Extramitochondrial cytochrome c is not the normal substrate for this enzyme, and the stimulatory effect is not specific for salts-a variety of agents which influence particle structure can promote this reaction (20). Honda, Robertson, and Gregory (9) have reported that the oxidation of reduced diphosphopyridine nucleotide (DPNH) by isolated beet root mitochondria is stimulated up to 50 % by low concentrations of salts, and they suggest that this effect may be responsible for the salt respiration of intact tissues. However, it is questionable whether or not extramitochondrial DPNH represents a physiological substrate, and further evidence on the mechanism of this effect is needed. In the course of an investigation of factors influencing the respiratory chain in sweet potato mitochondria, it was discovered that the DPNH oxidase activity is stimulated dramatically by a variety of salts. These effects are examined here, with special reference to some related salt-induced modifications of the particle structure. Preliminary reports on this work have already appeared (6, 7).