Biomaterial Database

Use of (3H) and (125I) tracers in steroid radioimmunoassays. 1975

S L Jeffcoate

The comparative use of 3H and 125I tracers in steroid radioimmunoassays will be discussed around the following points: 1. 3H. a) CONCLUSIONS they can be purchased commercially and have a long shelf-life. b) Disadvantages: they may have reduced affinity for antibodies due to "isotope effects"; the counting of beta-emitters is more expensive and difficult; 3H tracers are not available for all steroids. 2. 125I. a) CONCLUSIONS gamma-counting is cheaper, simpler and more precise; 125I tracers may have higher affinity for antibodies than unlabelled steroids; 125I can be used to label any steroid. b) Disadvantages: 125I tracers have a limited shelf-life (n.b. six months for 125I histamine tracers). The high affinity of some tracers will be a big disadvantage if the unlabelled steroid cannot compete effectively.

UI	MeSH Term	Description	Entries
D007457	Iodine Radioisotopes	Unstable isotopes of iodine that decay or disintegrate emitting radiation. I atoms with atomic weights 117-139, except I 127, are radioactive iodine isotopes.	Radioisotopes, Iodine
D011863	Radioimmunoassay	Classic quantitative assay for detection of antigen-antibody reactions using a radioactively labeled substance (radioligand) either directly or indirectly to measure the binding of the unlabeled substance to a specific antibody or other receptor system. Non-immunogenic substances (e.g., haptens) can be measured if coupled to larger carrier proteins (e.g., bovine gamma-globulin or human serum albumin) capable of inducing antibody formation.	Radioimmunoassays
D006207	Half-Life	The time it takes for a substance (drug, radioactive nuclide, or other) to lose half of its pharmacologic, physiologic, or radiologic activity.	Halflife,Half Life,Half-Lifes,Halflifes
D000918	Antibody Specificity	The property of antibodies which enables them to react with some ANTIGENIC DETERMINANTS and not with others. Specificity is dependent on chemical composition, physical forces, and molecular structure at the binding site.	Antibody Specificities,Specificities, Antibody,Specificity, Antibody
D013256	Steroids	A group of polycyclic compounds closely related biochemically to TERPENES. They include cholesterol, numerous hormones, precursors of certain vitamins, bile acids, alcohols (STEROLS), and certain natural drugs and poisons. Steroids have a common nucleus, a fused, reduced 17-carbon atom ring system, cyclopentanoperhydrophenanthrene. Most steroids also have two methyl groups and an aliphatic side-chain attached to the nucleus. (From Hawley's Condensed Chemical Dictionary, 11th ed)	Steroid,Catatoxic Steroids,Steroids, Catatoxic
D014316	Tritium	The radioactive isotope of hydrogen also known as hydrogen-3. It contains two NEUTRONS and one PROTON in its nucleus and decays to produce low energy BETA PARTICLES.	Hydrogen-3,Hydrogen 3