Energy-linked swelling of biotin-deficient rat liver mitochondria

Biotin-deficient rat liver mitochondria showed decreased phosphorylation efficiency as well as poor repiratory control as compared to normal rat liver mitochondria when NAD +-linked substrates were oxidized, but not when succinate was oxidized indicating a damage at the energy-conservation site I. Morphologically, the deficient mitochondria were indistinguishable from normal mitochondria. Except for reductions of NAD + and coenzyme Q, the molar ratios of the other respiratory components were unchanged. Additional evidence in favor of the defect at energy-conservation site I was obtained using the energy-linked swelling of mitochondria. No differences in the swelling pattern were observed between the normal and the deficient mitochondria when all the sites were operative or when energy changes were restricted to sites II and III. However, when the energy changes were restricted specifically to site I, the deficient mitochondria showed very poor swelling as compared to the normal preparation. When the swelling was mediated by externally added ATP, no difference was observed. The results indicate that the locus of damage in energy conservation at site I is related to the synthesis of the high-energy intermediate rather than its utilization.