The apparent ionization constants of the phenolic hydroxyl groups of thyroxine and related compounds

Gemmill, Chalmers L.

doi:10.1016/0003-9861(55)90048-5

Cited by 119 publications

(25 citation statements)

References 8 publications

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“…The two regions of the pH profile suggest an apparent deprotonation of a group with a pK a of 6.6 and protonation of a group with a pK a of 8.7 for maximum affinity. The pK a of the phenol in I 2 -Tyr has been reported as 6.4 and 6.5 (38,39). These values are quite similar to the value measured from the pH dependence of binding to hIYD and consistent with a preferential association of hIYD with the phenolate form of the halotyrosines.…”

Section: Discussionmentioning

confidence: 99%

A Switch between One- and Two-electron Chemistry of the Human Flavoprotein Iodotyrosine Deiodinase Is Controlled by Substrate

Chuenchor

Rokita

2015

Journal of Biological Chemistry

240

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Background: Iodotyrosine deiodinase utilizes FMN to maintain iodide homeostasis by reductive deiodination of iodotyrosine. Results: Crystallographic, pH, and redox studies demonstrate the role of substrate in organizing the active site for effective catalysis. Conclusion:Stepwise single electron transfer is promoted only after coordination of a halotyrosine within iodotyrosine deiodinase. Significance: A synergy between substrate selectivity and catalytic activity is created by the enzyme.

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Section: Discussionmentioning

confidence: 99%

A Switch between One- and Two-electron Chemistry of the Human Flavoprotein Iodotyrosine Deiodinase Is Controlled by Substrate

Chuenchor

Rokita

2015

Journal of Biological Chemistry

240

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“…The gravimetric concentration of T8 in the preparation was verified by its absorbance at 320 mun using the known molar extinction coefficient previously determined by Gemmill (20). The accuracy of the dilution of the final Ta preparation to be added to serum was monitored by tracer Ta.…”

Section: Introductionmentioning

confidence: 99%

Direct immunoassay of triiodothyronine in human serum

Larsen¹

1972

J. Clin. Invest.

209

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A B S T R A C T A sensitive and precise radioimmunoassay for the direct measurement of triiodothyronine (Ts) in human serum has been designed using sodium salicylate to block Ts-TBG binding. This assay is sufficiently sensitive to quantitate Ts accurately in 50-100 Al of normal serum and to measure quantities as small as 12.5 pg in 0.2 ml of hypothyroid serum. The Ts values observed in euthyroid subjects and in patients with various thyroid diseases are as follows: euthyroid (38) 1.10±0.25 (SD) ng/ml, hypothyroid (25) 0.39 +-0.21 (SD) ng/ml, and hyperthyroid (24) 5.46±4.42 (SD) ng/ml. The levels of Ts parallel the thyroxine (T4) concentration in the sera of these subjects. In eight pregnant women at the time of delivery, T3 concentrations were in the upper normal range (mean 1.33 ng/ml). The levels of Ts in cord serum obtained at the time of delivery of these patients (mean 0.53 ng/ml) are distinctly lower and close to the hypothyroid mean.Administration of 10 U of bovine thyroid-stimulating hormone (TSH) to euthyroid subjects causes a twofold increase in serum Ts levels within 8 hr. At this time, the increase in serum T4 concentration is only 41%. In two subjects in whom thyroid secretion was acutely inhibited, one after pituitary surgery and another after thyroidectomy, the serum T3 fell into the hypothyroid range within 1-2 days. Thus, serum T3 concentrations appear to be a sensitive index of acute changes in thyroid hormone secretion and should prove to be a useful adjunct to both the clinical and physiological evaluation of thyroid function.

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“…With the unexplained exceptions of the Schwarz-Mann and the Mann Research compounds, preparations giving the higher assay figures have the higher molar absorbances. These latter values approach 6.1 which is less than the figure of 6.207 found by Gemmill (1955). Unfortunately, no details of the quality of Gemmill's ('Bios') preparation are given.…”

Section: Kit Stated Normal Range Determined Normal Rangementioning

confidence: 69%

Accuracy and Standardisation of Serum Thyroxine Assays

1974

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Serum thyroxine was assayed concurrently by at least two of three different radio-displacement analysis kits—‘Tetralute’ (Ames), ‘Tetrasorb’ (Abbott) and ‘Thyopac-4’ (Radiochemical Centre). Repeated and careful cross checking by each of the methods was carried out on the ‘standard’ sera supplied with the kits and on other commercially available control sera. Differences of −3 to + 32% in apparent T-4 concentration were found. An unacceptable variability in T-4 content amongst batches of the same control sera was also evident which can be explained only by a lack of constancy in the commercial serum T-4 ‘standards’. The molar extinction coefficients, water and tri-iodothyronine contents of commercial ‘pure’ thyroxine preparations indicate purities of 89–99 %. An examination of published ‘euthyroid’ ranges and those found by the ‘kit’ radiometric methods suggests that many normal serum T-4 values are based on the use of an impure primary or doubtful secondary standard. A primary standardisation of the assay with thyroxine of known purity and of known concentration, as determined from its molar extinction at 324 nm is advocated. Using this procedure, the normal euthyroid range for serum T-4 is 55–148 nmol T4/1 (2.8–7.5 μg T-4I/100 ml) or close to it—in agreement with the earlier findings of Howarth and Maclagan (1969) and Ekins et al. (1969). During the period studied, ‘Tetralute’ produced the most accurate results.

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The apparent ionization constants of the phenolic hydroxyl groups of thyroxine and related compounds

Cited by 119 publications

References 8 publications

A Switch between One- and Two-electron Chemistry of the Human Flavoprotein Iodotyrosine Deiodinase Is Controlled by Substrate

A Switch between One- and Two-electron Chemistry of the Human Flavoprotein Iodotyrosine Deiodinase Is Controlled by Substrate

Direct immunoassay of triiodothyronine in human serum

Accuracy and Standardisation of Serum Thyroxine Assays

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