Thyroxine enzyme immunoassay

Comparison of EDso Values of Thyroxine (Tj) in Various Types of Heterologous and Homologous Enzyme Immunoassays of T4° fc... 

Fig. 6. Comparison of immunoassays using clonotype antibodies. The EDso values (thyroxine concentration corresponding to 50% of bound form at zero concentration of thyroxine) in thyroxine immunoassays using clonotype antithyroxine antibody prepared by fast protein liquid chromatography (FPLC). RIA, double-antibody radioimmunoassay FLA, fluorescence polarization immunoassay EIA, enzyme immunoassay. [Cited from Miyai et al. (M5).]...

Free Thyroxine. Measurement of free T4 radioimmunoassay in dried blood samples has been found to be useful to avoid false-positive results for low TBG in neonatal hypothyroid screening. Enzyme immunoassay of free T4 in serum was developed by Weetall et al. (W7) and subsequently by us (16). 

Fig. 8. A typical standard curve for enzyme immunoassay of free thyroxine in dried blood samples on filter paper. [Cited and modified from Hata et al. (H5). ]...

Gl. Galen, R. S., and Forman, D., Enzyme immunoassay of serum thyroxine with the AutoChemist multichannel analyzer. Clin. Chem. 23, 119—121 (1977). 

H4. Hata, N., Ito, M., Mizuta, H., Nose, O., and Miyai, K., Enzyme immunoassay of thyroxin-binding globulin in dried blood samples on filter paper. Clin. Chem. 29, 1437-1440 (1983). 

Y4. Yamamoto, R., Hattori, S., Inukai, T., Matsuura, A., Yamashita, K., Kosaka, A., and Kato, K., Enzyme immunoassay for thyroxine and triiodothyronine in human serum, with use of a covalent chromatographic separation method. Clin. Chem. 27, 1721-1723 (1981). 

EN19 Danielson, S.J., Brummond, B., Babb, B., Tyminski, P., Birecree, J., Fyles, J. and Pratt, L. (1991). Measurement of total thyroxine in serum or plasma by thin-film enzyme immunoassay. Clin. Chem. 37, 1034, Abstr. 594. 

ST32 Stahlschmidt, G.E., Smith, S.H., Miller, R.E. and Landt, M.L. (1987). The Stratus fluorometric enzyme immunoassay system evaluated for the determination of total thyroxine. Clin. Chem. 33, 883, Abstr. 17. 

ST49 Banfi, G., Racca, S., Daverio, R., Murone, M. and Bonini, P.A. (1989). Free thyroxin estimation by Stratus fluorometric enzyme immunoassay system. Biochim. Clin. 13, Suppl. 1/ 8, 133, Abstr. W 40. 

STN17 Raymond, A., Evans, I., Bowen, T., Trundle, S., Benham, M., Trundle, D. and Longhurst, S. (1991). Evaluation of a microparticle enzyme immunoassay for free thyroxine. Clin. Chem. 37, 963, Abstr. 253. 

Kunst A, Seidenschwarz E, Burk H, Schauer S, Haug H, Lehmann P, et al. New one-step enzyme immunoassay for free thyroxin. Clin Chem 1988 34 1830-3. 

Madsen K, Schulkamp K, Bellet N. Homogeneous enzyme immunoassay for the measurement of serum or plasma thyroxine. Clin Chem 1986 32 1163. 

McCormack G> Faix J. Evaluation of chemiluminescent enzyme immunoassay for thyroid binding globulin (TBG) and comparison of T4/TBG ratio with free thyroxin index. Clin Chem 1990 36 1149. 

H Arakawa, M Maeda, A Tsuji. Chemiluminescence enzyme immunoassay for thyroxin with the use of glucose oxidase and a bis(2,4,6-trichlorophenyl) oxalate-fluorescent dye system. Clin Chem 31 430, 1985. 

W22. Wood, W. G., Rohde, C, and Jacobs, A., A comparison of commercially available luminescence enhanced enzyme immunoassay with in-house non-radioisotopic assays for thyroxine binding globulin and total thyroxine. J. Clin. Chem. Clin. Biochem. 26, 135-140 (1988). 

A 3-maleimidobenzoyl derivative of L-thyroxine methyl ester has also been coupled to jS-D-galactosidase and used in an enzyme immunoassay of L-thyroxine. The procedures for the conjugation of rabbit immunoglobulin G and Fab antibodies with 3-D-galactosidase using AA -2-phenylene-dimaleimide have been improved by altering the reaction conditions. ... 

EEIA may be realized in different ways. Homogeneous (non-separation) enzyme immunoassay is based on the principle of modulation of activity of the enzyme label when an antigen binds to an antibody. This means that the activity of an enzyme label may be enhanced (activation) or suppressed (inhibition). In the first case, for instance, the attachment of a thyroxine to malate dehydrogenase causes an inhibition of the enzyme. This inhibition is, however, reversed when this conjugate binds... 

Enzyme immunoassays for digoxin, thyroxine and insulin have been performed with horse radish peroxidase as a label. The antigen-antibody complex was treated with luminol or other related hydrazides, the most efficient being 7-dimethylamino naphthalene-1,2-dicarboxylic acid hydrazide (92) (cf. p. 80) [129]. 

The EMMIA system was developed by Ngo and Lenhoff (N3, N4). In this assay, enzyme activity is modulated by an enzyme modulator which is coupled to antigen (free form) but not by the complex of enzyme modulator-antigen and antibody (bound form). As shown in Fig. 2 and Table 6, in an enzyme inhibitor immunoassay, an enzyme inhibitor is used as a negative modulator. For example, the reaction mixture for measuring thyroxine consists of acetylcholine inhibitor-thyroxine conjugate [I-Ag], acetylcholinesterase [E], unlabeled thyroxine [Ag], and antithyroxine antibody [Ab]. When the amount of unlabeled thyroxine, which binds to antibody [Ab Ag], is increased, the free form of acetylcholine inhibitor-thyroxine conjugate [I-Ag] increases, and the enzyme activity decreases. Therefore, the enzyme activity is inversely proportional to the concentration of unlabeled thyroxine. A tetrazyme kit (Abbott) is now available for measuring thyroxine. 

Standard radio-immunoassay procedures are applied, nowadays mainly solid phase assays which can be rapidly performed and evaluated, they are also several enzyme-linked immunoassay (ELISA) procedures from commercial suppliers. It is recommended to perform an internet check for the most appropriate method at the time of the study (for example DSL 2005). Methods have been described for triiodothyronine (Nejad et al. 1975, Chopra etal. 1972a, Larsen 1972a, 1972,) and for thyroxin (Chopra etal. 1971, Chopra 1972). The use of assays based on thyroxin binding globulin (Chopra et al. 1972b) is no longer recommended and cannot be applied to the rat, because the rat does not have this binding protein. However, for the human, measurement... 

Alkaline phosphatase is one of the most suitable enzymes for electrochemical immunoassays owing to its high turnover number and broad substrate specificity. Different substrates have been used, but 4-aminophenyl phosphate is most suitable, since the reaction product, 4-aminophenol is easily oxidized without fouling of the electrode surface. Thyroxine-binding globulin, cortisol, and prostatic acid phosphatase have been detected by using alkaline phosphatase. 

Finley, P.R. WiUiams, R.J. Lichti, D.A. Evaluation of a new homogeneous enzyme-inhibitor immunoassay of serum thyroxine with use of a bichromatic analyzer. Clin. Chem. 1980, 26, 1723-1726. 

Homogeneous immunoassay may serve as an example of a principal analytical approach realized by employing micellar systems [72,73] (Fig. 13). The enzyme (peroxidase) modified by hapten (thyroxine) has the same dependency profile of keat (wq) as the native enzyme (see Fig. 13). Formation of an immunocomplex (larger by size) in compliance with the principle of geometric correspondence results in a shift of the profile (wq) towards larger values of wq. At fixed values, immunocomplex formation can be denoted by a decrease in the observed reaction rate. Destruction of the immunocomplex, e.g., by introduction of free hapten, is detected by an increase in the observed enzymic activity. 

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