Purification and characterization of a cytosolic protein enhancing GSH-dependent microsomal iodothyronine...

A protein has been purified from rat liver cytosol which promoted GSH-responsive iodothyronine 5'-deiodinase activities in rat kidney microsomes. The factor behaved as a basic protein with an Mr of 11,000. It was active as a GSH-disulfide transhydrogenase with beta-hydroxyethyl disulfide as an acceptor and was also active in stimulating calf thymus ribonucleotide reductase with one-third the potency of native calf thymus glutaredoxin. Another basic protein, which degraded iodothyronines oxidatively, was also identified in the cytosolic preparations; this co-purified with soluble protein factor in the earlier purification stages and was partially separated from this factor by CM-cellulose chromatography. The glutaredoxin-like protein present in rat liver and kidney cytosol could provide a physiologic regulatory mechanism for GSH-dependent 5'-monodeiodination of iodothyronines.