Abstract
In confirmation of previous work enhancement of the fluorescence emission of reduced nicotinamide nucleotides in intact rat liver mitochondria was found to depend on incubation conditions. Under standard conditions the enhancement is constant at 4.8-fold in states 3 and 4 and is not altered by thyroidectomy of the animal 6 weeks prior to experiment. The ADP-induced (state 4----state 3----state 4) fluorescence changes are significantly different in intact mitochondria from normal and hypothyroid animals and reflect the decreased rate and efficiency of oxidative phosphorylation after thyroidectomy. Incubation of liver homogenates in vitro for 15 min with 1 microM triiodothyronine before isolating mitochondria significantly restores their ADP response towards normal. Direct addition of hormone to isolated mitochondria was ineffective. Enzymatic measurement of mitochondrial extracts shows that thyroidectomy leads to increases in the contents of NAD(H) by 22% and NADP(H) by 33%. With glutamate as substrate ADP-induced changes in the reduced/oxidized ratio of NAD+ are not significantly altered in hypothyroid preparations. By contrast the NADP+ ratio remains substantially more reduced in state 3 than it does in normal mitochondria. The hypothesis is advanced that the decreased efficiency of hypothyroid preparations in phosphorylating ADP may be the result of increased energy-linked transhydrogenase activity. This is needed to supply NADPH via the glutathione peroxidase for reducing endogenously formed peroxides. Direct reduction of mitochondrial glutathione with dithiothreitol had no substantial effect on ADP/O ratios or on ADP-induced redox cycles in either normal or thyroidectomised preparations. This decisively eliminates the possibility that lowered phosphorylation efficiency is the result of a leak of reducing equivalents via glutathione peroxidase.
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
