Preparation of $sup 125$I-labeled human thyroxine-binding alpha globulin and its turnover in normal and hypothyroid subjects

Journal Article · Tue Jul 01 04:00:00 EDT 1975 · J. Clin. Invest., v. 56, no. 1, pp. 79-87

DOI:https://doi.org/10.1172/JCI108082· OSTI ID:4038664

Cavalieri, R R; McMahon, F A; Castle, J N

A protein with the electrophoretic, immunologic, and hormone-binding properties of thyroxine-binding globulin (TBG) has been prepared from human plasma and labeled with radioiodine ($sup 125$I) by an enzymatic method of iodination. The [$sup 125$I]TBG retained the electrophoretic and immunologic characteristics of unlabeled TBG but exhibited a partial loss of thyroxine- binding activity, as assessed by affinity chromatography. The in vivo behavior of [$sup 125$I]TBG was studied in six euthyroid subjects (controls) with normal serum levels of TBG as measured both by radioimmunoassay and by determination of maximal T$sub 4$-binding capacity and in four male patients with untreated primary hyperthyroidism, three of whom had elevated serum TBG. The half-time of the final slope of the plasma disappearance curve averaged 5.0 days +- 1.2 (SD) in the controls and ranged from 3.9 to 10.9 days in the hypothyroid patients. The distribution volume was similar in the two groups, 6.7 +- 1.3 vs. 7.1 +- 2.1 liters. The catabolic clearance rate averaged 0.99 +- 0.33 liters plasma/24 h in the controls and 0.92 +- 0.46 in the hypothyroids. The absolute turnover rate of TBG, calculated from the catabolic clearance rate multiplied by the serum concentration of radioimmunoassayable TBG, averaged 17.8 +- 2.1 mg/day in the controls and ranged from 14.8 to 33.2 mg/day in the hypothyroids. Among the entire group of subjects there was no correlation between the serum TBG concentration and the absolute turnover rate of TBG. (auth)

• Research Organization: Veterans Administration Hospital, San Francisco
• Sponsoring Organization: USDOE
• NSA Number: NSA-33-029861
• OSTI ID: 4038664
• Journal Information: J. Clin. Invest., v. 56, no. 1, pp. 79-87, Journal Name: J. Clin. Invest., v. 56, no. 1, pp. 79-87; ISSN JCINA
• Country of Publication: United States
• Language: English

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