Mechanism of chilling injury in sweet potato Part XII. Temperature dependency of succinoxidase activity and lipid-protein interaction in mitochondria from healthy or chilling-stored tissue1

摘要

The Arrhenius plot of succinoxidase activity of intact mitochondria from healthy sweet potato (Ipomoea batatasLam.) roots showed two transition temperatures of the activation energy at 8–10°C and 16–18°C. Two transition temperatures were also observed in the case of sweet potatoes stored for 21 days at chilling temperature, but the activation energy was lower than that of healthy tissue. The results on lipiddepleted mitochondria and lipid-rebound mitochondria indicated that the membrane lipid played an important role in the transition temperature of succinoxidase activity. On the other hand, in the binding of phospholipid to lipid-depleted mitochondria from healthy tissue, the number of binding sites (n) and the dissociation constant (K) conspicuously changed at a temperature between 10 and 15°C. That is, n and K values above the temperature were considerably higher than those below the temperature, in spite of addition of phospholipid micelles whose phase transition temperatures were different from each other. In similar binding experiments with 14-day chilling-stored tissue, n values did not remarkably change, between higher and lower ranges of the above-mentioned temperature and were lower at higher than at lower temperature. The results suggest that the conformation of the protein moiety in the mitochondrial membrane undergoes reversible change in the early stage of chilling treatment, which becomes irreversible with prolonged chilling tre