On the role of NADPH and glutathione in the catalytic mechanism of hepatic thyroxine 5'-deiodination.

Sato, Tamotu; Maruyama, Shigeru; Nomura, Keiichi

doi:10.1507/endocrj1954.28.451

Cited by 8 publications

(5 citation statements)

References 25 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…Balsam and Ingbar (2) proposed that NADPH promoted T4 deiodination within cytosol, by increasing the concentration of GSH through the action of glutathione reductase, because NADPH did not show any effect on microsomal fraction. The results of the present study and of our previous observations (18,19) conflict with those of Balsam and Ingbar. Dose-dependent activation of NADPH is always greater than that of GSH and the additive effect of GSH to NADPH is not apparent (Fig.…”

Section: Discussioncontrasting

confidence: 99%

“…5D). The a d d i t i o n o f GSH t o graded doses o f MB, t h e b l o c k i n g a g e n t of NADPH, did not alter the dose-dependent inhibition of MB (18). These suggest that NADPH seems to accelerate directly T4 5'-deiodination and to be more rate-limiting as a cofactor of the reaction.…”

Section: Discussionmentioning

confidence: 81%

“…In contrast SH blocking agents such as thiouracil, N-5 ethylmaleinimide, iodoactamide andp-chloromercuribenzoate inhibit the reaction (5,10,13,14,(22)(23)(24). NADPH is also an important cofactor of T4 5'-deiodinase and changes in the enzyme activity are closely associated with the hexose-monophosphate pathway (2,10,18,19). In the fetal and neonatal period, hepatic T4 5'-monodeiodination is extremely low, which rises promptly after birth (3, 5, 9-1 1, 21, 25).…”

Section: Abbreviationsmentioning

confidence: 99%

See 2 more Smart Citations

Maturational Changes in the Regulatory Mechanisms of Hepatic Thyroxine 5'-Monodeiodination in Growing Rats

et al. 1983

Self Cite

View full text Add to dashboard Cite

SummaryChanges in the regulatory mechanisms of hepatic thyroxine (T4) 5'-monodeiodination during maturational process were studied in rats aged 1,3, and 6 wk andin adults. ~e s d i t e low T4 5'-deiodinase activity in the neonates, a similar degree of activation in older rats was obtained with graded doses of dithiothreitol. Lineweaver-Burk plot analysis showed that Vmax increased 1-3 wk of age, decreasing with age thereafter, whereas a high Km value in young rats (7.0-7.8 x M) fell to a level of 4.8 x lo-* M by 6 wk of age.T4 5'-deiodiiase at 3 wk of age was relatively resistant to iodoacetamide, a S H blocking agent (11% inhibition at M versus 47% in adult). Furthermore, it was markedly enhanced with 3 mM EDTA (125% versus 10-2Wo in older rats). Among various bivalent cations tested, Cu++ and Zn++ had a strong inhibitory effect on the reaction, whereas livers from 3-wk-old rats were less sensitive to Zn++ (7% inhibition at M versus 40% in adult). Responses to graded doses of reduced glutathione (GSH) or to its blocker, diamide, suggest that GSH exerts its promoting effect through preservation of protein S H radicals in reduced form. In contrast, NADPH stimulates the reaction directly, and a marked increase in the sensitivity to NADPH was observed 1-3 wk of age. Doseresponse relation to methylene blue (MB), inhibitor of NADPH, exhibited a biphasic effect on the reaction: stimulatory at smaller dose and inhibitory at larger dose. The critical dose of MB producing this reversal shifted to a lower level with advancing age, which appears to be due to the content of endogenous NADPH as well as to the reactivity of the enzyme to it. These results indicate that (1) protein S H radicals appear to change from a relatively inactive to an active state with age, in which an interaction with Zn++ might be involved; (2) GSH is probably associated with the conversion of S H groups; (3) NADPH enhances directly the --enzyme activity, playing a pivotal role in the regulation of the reaction; and (4) maturation of T4 5'-deiodination includes changes in the protein SH groups and GSH-NADPH generating system.

show abstract

Section: Discussioncontrasting

confidence: 99%

Section: Discussionmentioning

confidence: 81%

Section: Abbreviationsmentioning

confidence: 99%

See 1 more Smart Citation

Maturational Changes in the Regulatory Mechanisms of Hepatic Thyroxine 5'-Monodeiodination in Growing Rats

et al. 1983

Self Cite

View full text Add to dashboard Cite

show abstract

“…The low T3 state is compounded by a low tissue uptake of T4. The diminished deiodinase activity is either a primary enzyme defect or a defect of its co--factors NADPH or Glutathione (12).…”

Section: The Non Thyroid Illness Syndrome (Ntis)mentioning

confidence: 99%

Thyroid Emergencies

Bondugulapati¹,

Adlan²,

Premawardhana

2011

Sri Lanka J Crit Care

View full text Add to dashboard Cite

“…However, the physiological relevance of GSH could not be supported by dietary manipulation of hepatic GSH levels [7] or experiments in which the GSH concentration in cultured hepatocytes was drastically reduced without significant reduction of deiodinase activity [8]. Other experiments in which NADPH or GSH were added to stored homogenates indicated that NADPH had a stimulatory effect on microsomal deiodinase quite apart from its involvement in the reduction of GSSG by glutathione reductase [9]. Hence, as reviewed in detail elsewhere [10,11], the precise role of GSH in relation to the regulation of 5'-deiodination in vivo has been controversial.…”

Section: Introductionmentioning

confidence: 99%

NADPH-dependent generation of a cytosolic dithiol which activates hepatic iodothyronine 5′-deiodinase. Demonstration by alkylation with iodoacetamide

Das¹,

Hummel²,

Walfish³

1986

Biochemical Journal

View full text Add to dashboard Cite

We have assessed a previously proposed mechanism mediating 5'-deiodinase activation involving enzymic reduction of disulphides to thiols in non-glutathione cytosolic components of Mr approx. 13,000 (Fraction B) catalysed by NADPH in the presence of other cytosolic components of Mr greater than 60,000 (Fraction A). The extent of Fraction B reduction under various experimental conditions was monitored by determining the amount of 14C incorporated into chromatographically isolated Fractions B and A after their alkylation with iodo[14C]acetamide. Incorporation of 14C into B was found to require the simultaneous presence of NADPH and A, to be directly proportional to the concentration of NADPH added, and to be unaffected by either propylthiouracil or iopanoate. Activation of 5'-deiodinase attainable using B after its partial reduction by various concentrations of NADPH and subsequent alkylation with non-radioactive iodoacetamide was inversely proportional to the previously added concentration of NADPH. Fraction B was stable at 100 degrees C for 5 min, while similar heat treatment of Fraction A or omission of NADPH resulted in a complete loss of 14C incorporation. A greater than 90% reduction in iodo[14C]acetamide incorporation was revealed when 0.2 mM-sodium arsenite was added after enzymic reduction of B, as well as when NADPH was replaced by NADH. Fraction B could be labelled more extensively after reduction non-specifically, with dithiothreitol or NaBH4, but not by GSH. These observations provide strong evidence for the presence in vivo of a cytosolic disulphide (DFBS2) in Fraction B which can be reduced enzymically to a dithiol [DFB(SH)2] by NADPH and cytosolic components in Fraction A. The degree of activation of hepatic 5'-deiodinase correlated with the amount of available (unalkylated) Fraction B.

show abstract

On the role of NADPH and glutathione in the catalytic mechanism of hepatic thyroxine 5'-deiodination.

Cited by 8 publications

References 25 publications

Maturational Changes in the Regulatory Mechanisms of Hepatic Thyroxine 5'-Monodeiodination in Growing Rats

Maturational Changes in the Regulatory Mechanisms of Hepatic Thyroxine 5'-Monodeiodination in Growing Rats

Thyroid Emergencies

NADPH-dependent generation of a cytosolic dithiol which activates hepatic iodothyronine 5′-deiodinase. Demonstration by alkylation with iodoacetamide

Contact Info

Product

Resources

About