Generated Dihydrolipoamide and Cytosolic Components Stimulate Hepatic Microsomal Thyroxine 5’-Deiodination: Similar Effects of Cytosolic Components on Other Sulfhydryl Compounds
5′-deiodinase (5′-DI) is a thiol-dependent enzyme (1,2) and sulfhydryl compounds, such as dithiothreitol (DTT), 2-mercaptoethanol (2-ME), and reduced glutathione (GSH, molecular weight [M.W.] 307 Da.) have been shown to function as activators by acting as direct reductants of the enzyme SH groups oxidized during deiodination. While several investigators have reported that isolated hepatic microsomes have very little 5′-DI activity in the absence of added thiols, reconstitution with cytosol has been reported to enhance 5′-DI activity, suggesting that cytosol contains one or more unidentified factors which are involved in 5′-deiodination (3). Recently, we have reported that cytosolic components of approximate M.W. 13,000 Da. (fraction B), which we have assigned an equivalent abbreviation of IMCC, might play a role as a direct reductant in an NADPH-dependent non-glutathione cytosolic reductase system (4). Hence, while sulfhydryl compounds may act directly with the 5′-DI, it is also possible that endogenous cytosolic factors may function as regulatory intermediaries between the enzyme and sulfydryl compounds, and that the overall influence of such compounds on 5′-DI may be mediated by such cytosolic cofactors.
KeywordsDirect Reductant Hepatic Microsome Sulfhydryl Compound Cytosolic Component Intermediate Molecular Weight
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- 4.Sawada K, Hummel BCW, and Walfish PG. Prog, and Absts. of 57th Annual Meeting of the Endocrine Society, Baltimore, MD, 1985, p 278.Google Scholar