Insulin-status-dependent modulation of FoF₁ ATPase activity in rat kidney mitochondria

The early and late effects of alloxan-diabetes and insulin treatment on kinetic properties of mitochondrial FoF₁ ATPase were examined. Diabetic state resulted in significant decrease in the activity while insulin treatment caused hyper-stimulation. In control animals the enzyme activity resolved in three kinetic components. In diabetic condition only component I and II were present. With insulin treatment component III was restored but component II was abolished. Diabetic state and insulin treatment had varied effects on K_m values of the three components, whereas the V _max values were generally on the higher side. Evaluation of the ^AppK_cat/K_m values revealed that diabetic state resulted in increased catalytic efficiency; insulin treatment brought back these values to normality. Temperature kinetics studies indicated that the phase transition temperature decreased significantly in the diabetic and insulin-treated diabetic animals. The energy of activation in low temperature range increased in the diabetic animals. Insulin treatment corrected the Arrhenius pattern at early stage of diabetes; at late stage the pattern was reversed. The results are suggestive of subtle insulin-status-dependent alterations in membrane structure - function relationships.