The role of
adenine nucleotide translocase (AdNT) in the reduced oxidative metabolism of
hypothyroidism has been examined. Both AdNT and respiratory activities in liver mitochondria of thyroidectomized rats were 30% below normal. Mitochondrial AdNT activities were determined by the back-exchange method of Pfaff and Klingenberg (Eur. J. Biochem. 6, 66, 1968). The Km and Vmax of the
enzyme were temperature dependent. At physiological temperature, the Km and Vmax of the normal rat AdNT were 10 microM (for external
ADP) and 4.73% s-1 (percentage efflux of the labeled
adenine nucleotides), respectively. AdNT in hypothyroid rat liver mitochondria exhibited a 25-35% lower Vmax and 75% higher Km when assayed over the temperature range 0 to 37 degrees C. Dixonplot studies indicated that the AdNT in
hypothyroidism was two- to threefold more sensitive to
atractylate and
palmitoyl-CoA inhibitions. In contrast the
ADP-
ATP translocase in
hypothyroidism was more resistant than the control carrier to
bongkrekate inhibition. The decrease in the transport of
ADP, which is consistent with the decreased oxidative activity associated with
hypothyroidism, apparently occurs secondary to changes in the
lipid matrix of the inner mitochondrial membrane (F. L. Hoch (1977) Arch. Biochem. Biophys. 178, 535.).