title: The rapid response of isolated mitochondrial particles to 0.1 nM-tri-iodothyronine correlates with the ADP-ribosylation of a single inner-membrane protein.
abstract: Under defined conditions liver mitochondria from hypothyroid rats show an apparent lowering of the ADP/O ratio, which can be corrected by addition in vitro of 0.1 nM-tri-iodothyronine (T3). Nicotinamide prevents this restoration by hormone, lowers the ADP/O ratio of euthyroid-rat mitochondria to hypothyroid-rat values and induces T3-sensitivity in euthyroid-rat mitoplasts indistinguishable from that found with hypothyroid-rat preparations. Incorporation into the trichloroacetic-acid insoluble fraction of mitoplasts and hypothyroid-rat mitochondria of radiolabel from [adenine-14C]-NAD+ was stimulated by T3: this stimulation was abolished by nicotinamide. The findings strongly suggest that this incorporation occurs external to the matrix. Confirming the work of others, PAGE of radiolabelled mitoplasts shows alkali-labile modification of a major species of approx. 30 kDa: both nicotinamide and T3 abolish this modification. By contrast, T3 promotes incorporation of label into a single major 11 kDa species: this incorporated label is somewhat acid-labile, and the incorporation is abolished by nicotinamide. Comparative electrophoresis of purified sub-mitoplast fractions show that the 11 kDa species is in the inner membrane and absent from the matrix. The findings are consistent with a receptor-mediated ADP-ribosylation mechanism for the rapid action of T3 on mitochondria.
authors.affiliation: Department of Biochemistry and Molecular Biology, University College London, U.K.
authors.forename: D L
authors.initials: DL
authors.lastname: Hardy
authors.forename: J
authors.initials: J
authors.lastname: Mowbray
mesh_terms: D000244:Adenosine Diphosphate / Q000378:metabolism; D000246:Adenosine Diphosphate Ribose / Q000378:metabolism*; D000818:Animals; D011232:Chemical Precipitation; D004591:Electrophoresis, Polyacrylamide Gel; D006863:Hydrogen-Ion Concentration; D007037:Hypothyroidism / Q000139:chemically induced / Q000378:metabolism; D007700:Kinetics; D008297:Male; D008565:Membrane Proteins / Q000378:metabolism*; D008930:Mitochondria, Liver / Q000187:drug effects / Q000378:metabolism*; D009243:NAD / Q000378:metabolism; D009536:Niacinamide / Q000494:pharmacology; D010101:Oxygen Consumption / Q000187:drug effects; D011441:Propylthiouracil; D051381:Rats; D011919:Rats, Inbred Strains; D014284:Triiodothyronine / Q000494:pharmacology*
chemical_list: D008565:Membrane Proteins; D014284:Triiodothyronine; D009243:NAD; D000246:Adenosine Diphosphate Ribose; D009536:Niacinamide; D000244:Adenosine Diphosphate; D011441:Propylthiouracil