title: Rat hepatic and renal 5'-deiodination of rT3 during fasting: supportive role of intermediate Mr cytosolic non-glutathione thiol cofactor and NADPH.
abstract: The roles of subcellular components and, in particular, cytosol fractions and beta-nicotinamide adenine dinucleotide phosphate, reduced form (NADPH), in the regulation of rat hepatic and renal 5'-deiodination during fasting were assessed. 5'-deiodinase (5'-DI) activities in reaction mixtures were measured by using outer ring 125I-radiolabelled reverse triiodothyronine (rT3) as a substrate in the presence of 200 mumol/L NADPH. Subcellular components from rats fed ad libitum or fasted for 24, 48 or 72 hours were prepared by standard differential centrifugation. Cytosol was chromatographed on a Sephadex G-50 column to obtain Fraction A of molecular weight (Mr) greater than 60,000 and Fraction B of Mr approximately 13,000 and to exclude reduced glutathione (GSH) (Mr less than 400). 5'-DI activity in liver homogenates was reduced by 42% at 24 hours and by 59% at 48 hours of fasting. In reconstitution experiments, liver microsomes showed a progressive loss of 5'-DI activity, reaching a maximal reduction of 46% at 72 hours of fasting. Activation of microsomal deiodinase by whole liver cytosol was also significantly reduced at 24 hours of fasting and achieved a maximal reduction of 5'-DI activation of 42% at 48 hours before substantial but incomplete recovery at 72 hours. Cytosolic Fraction A and B were assessed in combination with fed microsomes and NADPH. A close correlation was demonstrated between the loss of hepatic 5'-DI supportive activity in whole cytosol and that of Fraction B but not A during fasting.(ABSTRACT TRUNCATED AT 250 WORDS)
authors.affiliation: Thyroid Research Laboratory, Mount Sinai Hospital, Toronto, Ontario, Canada.
authors.forename: K
authors.initials: K
authors.lastname: Iwase
authors.forename: B C
authors.initials: BC
authors.lastname: Hummel
authors.forename: P G
authors.initials: PG
authors.lastname: Walfish
mesh_terms: D000818:Animals; D003600:Cytosol / Q000378:metabolism; D005215:Fasting; D007453:Iodide Peroxidase / Q000378:metabolism*; D007668:Kidney / Q000201:enzymology / Q000378:metabolism*; D008297:Male; D008862:Microsomes, Liver / Q000201:enzymology / Q000378:metabolism*; D009249:NADP / Q000494:pharmacology*; D010084:Oxidation-Reduction; D051381:Rats; D011919:Rats, Inbred Strains; D013438:Sulfhydryl Compounds / Q000032:analysis*; D013963:Thyroid Hormones / Q000097:blood; D014284:Triiodothyronine / Q000378:metabolism*
chemical_list: D013438:Sulfhydryl Compounds; D013963:Thyroid Hormones; D014284:Triiodothyronine; D009249:NADP; D007453:Iodide Peroxidase