3',5'-Diiodothyronine to 3'-monoiodothyronine conversion in the fed and fasted rat

Enzyme characteristics and evidence for two distinct 5'-deiodinases

Robert Christian Smallridge, K. D. Burman, K. E. Ward, L. Wartofsky, R. C. Dimond, F. D. Wright, K. R. Latham

Research output: Contribution to journalArticle

28 Citations (Scopus)

Abstract

The present study investigated the 5'-monodeiodination of 3',5'-diiodothyronine (3',5'T 2) to 3'-monoiodothyronine (3'T 1), a reaction involving deiodination at the same position as is needed for T 4 to T 3 and for rT 3 to 3,3'-diiodothyronine (3,3'T 2) conversion. 3',5'T 2 to 3'T 1 conversion appears to be enzymatic in nature, being dependent on temperature and pH. Consistent with previous observations for T 4 and rT 3, 3',5'T 2 5'-deiodination occurred primarily in the liver and kidney, but, unlike these other iodothyronines, 3',5'T 2 to 3'T 1 conversion was active in cytosol as well as in microsomes. Characteristics of the microsomal enzymatic activity included heat inactivation (56°C), a broad pH plateau (pH 4.9-7.6), and an apparent K(m) of 8.6 x 10 -9 M. Cytosolic activity occurred with a narrower pH peak (pH 5-6.5), and had a different apparent K(m) of 2.4 x 10 -7 M. The activity of both subcellular enzymes was inhibited by iopanoic acid and prophylthiouracil. Dithiothreitol, while stimulating a 5- to 7-fold increase in microsomal 3',5'T 2 5'-deiodination, produced less than a 2-fold increase in cytosol activity. Fasting, a condition known to inhibit both T 4 and rT 3 5'-deiodination, produced a 68% decrease (1.16 ± 0.29 vs. 3.61 ± 0.97 ng/mg protein; mean ± SE) in hepatic T 4 to T 3 conversion, yet had no effect on 3',5'T 2 to 3'T 1 conversion in rat liver or kidney homogenates. Cellular fractionation studies indicated that liver microsomal 3',5'T 2 deiodination was diminished by 46% (71.6 ± 19.8 vs. 131.6 ± 14.4 pg/mg protein; P < 0.025) after a 3-day fast, whereas cytosol activity was unchanged (23.7 ± 10.2 vs. 22.8 ± 4.9 pg/mg protein). Treatment with T 4 (0.8 μg/100 g BW.day) failed to correct the reduced 3',5'T 2 5'-deiodinase activity in microsomes from fasted rats [79.7 ± 17.4 (fasted) vs. 311.9 ± 33.8 (control) pg/mg protein; P < 0.001]. However, the addition of 5 mM dithiothreitol to the incubation medium increased hepatic microsomal 5'-deiodinase activity for 3',5'T 2 7- and 12-fold in the fed and fasted animals, respectively. These results indicate that: 3',5'T 2 to 3'T 3 conversion proceeds enzymatically in liver and kidney, enzyme activities having different kinetics exist in both micromes and cytosol, fasting inhibits 3',5'T 2 deiodination in microsomes but not in homogenates or cytosol, and microsomal activity is restored by a sulfhydryl group-reducing agent, but not by physiological doses of T 4. The data strongly suggest the existence of more than one 3',5'T 2 5'-deiodinase in rat liver and kidney.

Original languageEnglish (US)
Pages (from-to)2336-2345
Number of pages10
JournalEndocrinology
Volume108
Issue number6
StatePublished - 1981
Externally publishedYes

Fingerprint

Iodide Peroxidase
Cytosol
Liver
Enzymes
Microsomes
Kidney
Dithiothreitol
Fasting
Proteins
Iopanoic Acid
Reducing Agents
3',5'-diiodothyronine
3'-monoiodothyronine
Hot Temperature
Temperature

ASJC Scopus subject areas

  • Endocrinology
  • Endocrinology, Diabetes and Metabolism

Cite this

Smallridge, R. C., Burman, K. D., Ward, K. E., Wartofsky, L., Dimond, R. C., Wright, F. D., & Latham, K. R. (1981). 3',5'-Diiodothyronine to 3'-monoiodothyronine conversion in the fed and fasted rat: Enzyme characteristics and evidence for two distinct 5'-deiodinases. Endocrinology, 108(6), 2336-2345.

3',5'-Diiodothyronine to 3'-monoiodothyronine conversion in the fed and fasted rat : Enzyme characteristics and evidence for two distinct 5'-deiodinases. / Smallridge, Robert Christian; Burman, K. D.; Ward, K. E.; Wartofsky, L.; Dimond, R. C.; Wright, F. D.; Latham, K. R.

In: Endocrinology, Vol. 108, No. 6, 1981, p. 2336-2345.

Research output: Contribution to journalArticle

Smallridge, Robert Christian ; Burman, K. D. ; Ward, K. E. ; Wartofsky, L. ; Dimond, R. C. ; Wright, F. D. ; Latham, K. R. / 3',5'-Diiodothyronine to 3'-monoiodothyronine conversion in the fed and fasted rat : Enzyme characteristics and evidence for two distinct 5'-deiodinases. In: Endocrinology. 1981 ; Vol. 108, No. 6. pp. 2336-2345.
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abstract = "The present study investigated the 5'-monodeiodination of 3',5'-diiodothyronine (3',5'T 2) to 3'-monoiodothyronine (3'T 1), a reaction involving deiodination at the same position as is needed for T 4 to T 3 and for rT 3 to 3,3'-diiodothyronine (3,3'T 2) conversion. 3',5'T 2 to 3'T 1 conversion appears to be enzymatic in nature, being dependent on temperature and pH. Consistent with previous observations for T 4 and rT 3, 3',5'T 2 5'-deiodination occurred primarily in the liver and kidney, but, unlike these other iodothyronines, 3',5'T 2 to 3'T 1 conversion was active in cytosol as well as in microsomes. Characteristics of the microsomal enzymatic activity included heat inactivation (56°C), a broad pH plateau (pH 4.9-7.6), and an apparent K(m) of 8.6 x 10 -9 M. Cytosolic activity occurred with a narrower pH peak (pH 5-6.5), and had a different apparent K(m) of 2.4 x 10 -7 M. The activity of both subcellular enzymes was inhibited by iopanoic acid and prophylthiouracil. Dithiothreitol, while stimulating a 5- to 7-fold increase in microsomal 3',5'T 2 5'-deiodination, produced less than a 2-fold increase in cytosol activity. Fasting, a condition known to inhibit both T 4 and rT 3 5'-deiodination, produced a 68{\%} decrease (1.16 ± 0.29 vs. 3.61 ± 0.97 ng/mg protein; mean ± SE) in hepatic T 4 to T 3 conversion, yet had no effect on 3',5'T 2 to 3'T 1 conversion in rat liver or kidney homogenates. Cellular fractionation studies indicated that liver microsomal 3',5'T 2 deiodination was diminished by 46{\%} (71.6 ± 19.8 vs. 131.6 ± 14.4 pg/mg protein; P < 0.025) after a 3-day fast, whereas cytosol activity was unchanged (23.7 ± 10.2 vs. 22.8 ± 4.9 pg/mg protein). Treatment with T 4 (0.8 μg/100 g BW.day) failed to correct the reduced 3',5'T 2 5'-deiodinase activity in microsomes from fasted rats [79.7 ± 17.4 (fasted) vs. 311.9 ± 33.8 (control) pg/mg protein; P < 0.001]. However, the addition of 5 mM dithiothreitol to the incubation medium increased hepatic microsomal 5'-deiodinase activity for 3',5'T 2 7- and 12-fold in the fed and fasted animals, respectively. These results indicate that: 3',5'T 2 to 3'T 3 conversion proceeds enzymatically in liver and kidney, enzyme activities having different kinetics exist in both micromes and cytosol, fasting inhibits 3',5'T 2 deiodination in microsomes but not in homogenates or cytosol, and microsomal activity is restored by a sulfhydryl group-reducing agent, but not by physiological doses of T 4. The data strongly suggest the existence of more than one 3',5'T 2 5'-deiodinase in rat liver and kidney.",
author = "Smallridge, {Robert Christian} and Burman, {K. D.} and Ward, {K. E.} and L. Wartofsky and Dimond, {R. C.} and Wright, {F. D.} and Latham, {K. R.}",
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TY - JOUR

T1 - 3',5'-Diiodothyronine to 3'-monoiodothyronine conversion in the fed and fasted rat

T2 - Enzyme characteristics and evidence for two distinct 5'-deiodinases

AU - Smallridge, Robert Christian

AU - Burman, K. D.

AU - Ward, K. E.

AU - Wartofsky, L.

AU - Dimond, R. C.

AU - Wright, F. D.

AU - Latham, K. R.

PY - 1981

Y1 - 1981

N2 - The present study investigated the 5'-monodeiodination of 3',5'-diiodothyronine (3',5'T 2) to 3'-monoiodothyronine (3'T 1), a reaction involving deiodination at the same position as is needed for T 4 to T 3 and for rT 3 to 3,3'-diiodothyronine (3,3'T 2) conversion. 3',5'T 2 to 3'T 1 conversion appears to be enzymatic in nature, being dependent on temperature and pH. Consistent with previous observations for T 4 and rT 3, 3',5'T 2 5'-deiodination occurred primarily in the liver and kidney, but, unlike these other iodothyronines, 3',5'T 2 to 3'T 1 conversion was active in cytosol as well as in microsomes. Characteristics of the microsomal enzymatic activity included heat inactivation (56°C), a broad pH plateau (pH 4.9-7.6), and an apparent K(m) of 8.6 x 10 -9 M. Cytosolic activity occurred with a narrower pH peak (pH 5-6.5), and had a different apparent K(m) of 2.4 x 10 -7 M. The activity of both subcellular enzymes was inhibited by iopanoic acid and prophylthiouracil. Dithiothreitol, while stimulating a 5- to 7-fold increase in microsomal 3',5'T 2 5'-deiodination, produced less than a 2-fold increase in cytosol activity. Fasting, a condition known to inhibit both T 4 and rT 3 5'-deiodination, produced a 68% decrease (1.16 ± 0.29 vs. 3.61 ± 0.97 ng/mg protein; mean ± SE) in hepatic T 4 to T 3 conversion, yet had no effect on 3',5'T 2 to 3'T 1 conversion in rat liver or kidney homogenates. Cellular fractionation studies indicated that liver microsomal 3',5'T 2 deiodination was diminished by 46% (71.6 ± 19.8 vs. 131.6 ± 14.4 pg/mg protein; P < 0.025) after a 3-day fast, whereas cytosol activity was unchanged (23.7 ± 10.2 vs. 22.8 ± 4.9 pg/mg protein). Treatment with T 4 (0.8 μg/100 g BW.day) failed to correct the reduced 3',5'T 2 5'-deiodinase activity in microsomes from fasted rats [79.7 ± 17.4 (fasted) vs. 311.9 ± 33.8 (control) pg/mg protein; P < 0.001]. However, the addition of 5 mM dithiothreitol to the incubation medium increased hepatic microsomal 5'-deiodinase activity for 3',5'T 2 7- and 12-fold in the fed and fasted animals, respectively. These results indicate that: 3',5'T 2 to 3'T 3 conversion proceeds enzymatically in liver and kidney, enzyme activities having different kinetics exist in both micromes and cytosol, fasting inhibits 3',5'T 2 deiodination in microsomes but not in homogenates or cytosol, and microsomal activity is restored by a sulfhydryl group-reducing agent, but not by physiological doses of T 4. The data strongly suggest the existence of more than one 3',5'T 2 5'-deiodinase in rat liver and kidney.

AB - The present study investigated the 5'-monodeiodination of 3',5'-diiodothyronine (3',5'T 2) to 3'-monoiodothyronine (3'T 1), a reaction involving deiodination at the same position as is needed for T 4 to T 3 and for rT 3 to 3,3'-diiodothyronine (3,3'T 2) conversion. 3',5'T 2 to 3'T 1 conversion appears to be enzymatic in nature, being dependent on temperature and pH. Consistent with previous observations for T 4 and rT 3, 3',5'T 2 5'-deiodination occurred primarily in the liver and kidney, but, unlike these other iodothyronines, 3',5'T 2 to 3'T 1 conversion was active in cytosol as well as in microsomes. Characteristics of the microsomal enzymatic activity included heat inactivation (56°C), a broad pH plateau (pH 4.9-7.6), and an apparent K(m) of 8.6 x 10 -9 M. Cytosolic activity occurred with a narrower pH peak (pH 5-6.5), and had a different apparent K(m) of 2.4 x 10 -7 M. The activity of both subcellular enzymes was inhibited by iopanoic acid and prophylthiouracil. Dithiothreitol, while stimulating a 5- to 7-fold increase in microsomal 3',5'T 2 5'-deiodination, produced less than a 2-fold increase in cytosol activity. Fasting, a condition known to inhibit both T 4 and rT 3 5'-deiodination, produced a 68% decrease (1.16 ± 0.29 vs. 3.61 ± 0.97 ng/mg protein; mean ± SE) in hepatic T 4 to T 3 conversion, yet had no effect on 3',5'T 2 to 3'T 1 conversion in rat liver or kidney homogenates. Cellular fractionation studies indicated that liver microsomal 3',5'T 2 deiodination was diminished by 46% (71.6 ± 19.8 vs. 131.6 ± 14.4 pg/mg protein; P < 0.025) after a 3-day fast, whereas cytosol activity was unchanged (23.7 ± 10.2 vs. 22.8 ± 4.9 pg/mg protein). Treatment with T 4 (0.8 μg/100 g BW.day) failed to correct the reduced 3',5'T 2 5'-deiodinase activity in microsomes from fasted rats [79.7 ± 17.4 (fasted) vs. 311.9 ± 33.8 (control) pg/mg protein; P < 0.001]. However, the addition of 5 mM dithiothreitol to the incubation medium increased hepatic microsomal 5'-deiodinase activity for 3',5'T 2 7- and 12-fold in the fed and fasted animals, respectively. These results indicate that: 3',5'T 2 to 3'T 3 conversion proceeds enzymatically in liver and kidney, enzyme activities having different kinetics exist in both micromes and cytosol, fasting inhibits 3',5'T 2 deiodination in microsomes but not in homogenates or cytosol, and microsomal activity is restored by a sulfhydryl group-reducing agent, but not by physiological doses of T 4. The data strongly suggest the existence of more than one 3',5'T 2 5'-deiodinase in rat liver and kidney.

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