Type I collagen is thermally unstable at body temperature.

Measured by ultra-slow scanning calorimetry and isothermal circular dichroism, human lung collagen monomers denature at 37 degrees C within a couple of days. Their unfolding rate decreases exponentially at lower temperature, but complete unfolding is observed even below 36 degrees C. Refolding of full-length, native collagen triple helices does occur, but only below 30 degrees C. Thus, contrary to the widely held belief, the energetically preferred conformation of the main protein of bone and skin in physiological solution is a random coil rather than a triple helix. These observations suggest that once secreted from cells collagen helices would begin to unfold. We argue that initial microunfolding of their least stable domains would trigger self-assembly of fibers where the helices are protected from complete unfolding. Our data support an earlier hypothesis that in fibers collagen helices may melt and refold locally when needed, giving fibers their strength and elasticity. Apparently, Nature adjusts collagen hydroxyproline content to ensure that the melting temperature of triple helical monomers is several degrees below rather than above body temperature.

[Prospects for use of hapten-heterologous conjugates in immunoassay of thyroid hormones]. / Vozmozhnosti ispol'zovaniia gapten-geterologichnykh kon''iugatov v immunoanalize tiroidnykh gormonov.

The effect of hapten heterology on the characteristics of indirect ELISA methods for determination of thyroxine and triiodothyronine using monoclonal antibodies was studied. The use of the heterologous triiodothyronine-bovine serum albumin conjugate in immunoassays for thyroxine improved the sensitivity of these assays twofold and reduced the cross-reactivity with triiodothyronine from 1 to 0.5% as compared to the homologous variant. By contrast, the heterology in the immunoassays for triiodothyronine appeared inadequate. It was shown that the specificity and sensitivity of hapten immunoassays can be modulated by altering the chemical structure of the hapten-label conjugate, which is most evident in experiments with monoclonal antibodies.

[Preparing monoclonal antibodies to thyroxine]. / Poluchenie monokonal'nykh antitel k tiroksinu.

Spleen cells of BALB/c mouse immunized with the keyhole limpet haemocyanin and thyroxine conjugate were fused with P3-X63-Ag8.653 mouse myeloma cells to produce. Four monoclonal antibodies selected by indirect ELISA and partially characterized. One antibody, 1B7, chosen for immunoassay, was produced in mouse ascites fluid, purified and analyzed; it proved to belong to the IgG1 subclass. The cross-reactivity with triiodothyronine was less than 1%, the association constant was 3 x 10(9) M-1.