A sensitive manual enzyme immunoassay for thyroxine.

We describe an immunoassay for thyroxine in serum. In the assay specific antibody covalently bonded to latex particles is used, along with horseradish peroxidase as the label, and o-phenylenediamine as the chromogen. The flexible protocol is designed for manual execution. Performance is similar to that of the highest-sensitivity thyroxine radioimmunoassays. Results correlate well with radioimmunoassay (r = 0.99, slope = 0.93, y-intercept = 2.4 microgram/liter for 201 samples) and an automated enzyme immunoassay (r = 0.97, slope = 0.99, y-intercept = 4.7 coefficients of variation are less than 7.2% over the entire useful range of the assay (20--240 microgram/liter). The limit of detection is less than 94 pg/tube at 20 microgram/liter. Only D-thyroxine is known to interfere with serum assays. This assay has no discernible protein effect from 40 to 80 g of protein per liter, unlike many thyroxine radioimmunoassays. Serum preservatives known to be peroxidase inhibitors do not adversely affect assay performance because of the 56-fold dilution in the final assay mixture. Hemolyzed serum and EDTA-treated plasmas are unsuitable for this assay.

Energies of polypeptides: theoretical conformational study of polyglycine using quantum mechanical partitioning.

A method is developed for evaluating the total energy of polypeptides based on a combination of quantum mechanical and empirical potentials. Adjacent and nonadjacent peptide units are allowed to interact through these respective means. Our hybrid procedure is applied to a study of polyglycine and compared to the results obtained by the method of Scheraga and coworkers. We find the alpha helical conformation of a single strand of polyglycine to be most stable in vacuo. Other less-stable configurations include the 3(10) helix, the 2(7) ribbon structure, and the fully extended conformation.

Phosphorylation of nuclear proteins in rat regenerating liver.

In studies of the phosphorylated proteins in rat liver and Walker-256, it was established that the ratio of various fractions of P-N linkages to P-O linkages varies from 0.6 to 3.1. In rat regenerating liver nuclei, the ratio of P-N and P-O varies with time after partial hepatectomy. Using [3H]-lysine and 32Pi, it is shown that phosphoryllysine forms in some new and, presumably, some preexisting H1 molecules. Using [3H]histidine and 32Pi, it is shown that phosphohistidine forms exclusively in preexisting H4. The half-life of H4 phosphohistidine appears to be about 2 h.