[The biotin-thyroxin conjugate as a bifunctional ligand of binding proteins].

The conjugate of the residue of vitamin H (biotin, Bt) with the hormone of thyroid gland thyroxin (T4) was prepared by N-acylation of N-(3-aminopropyl) biotin amide with N-hydroxysuccinimide ester of N-acetyl thyroxin. The interactions of the Bt-T4 conjugate with one or simultaneously with two binding proteins with affinity to Bt or T4 in solution and on a solid phase were studied by electron spectroscopy, enzyme immunoassay, and computer modeling. Bt-T4 was specifically fixed in the Bt-binding site of the streptavidin molecule via a large number of hydrogen bonds and hydrophobic interactions.

[Precipitation of streptavidin complexes with biotinylated proteins in agar gel].

The effect of precipitation of complexes of streptavidin with biotinylated proteins under conditions of simple (according to Mancini) and double (according to Ouchterlony) radial diffusion in agar gel was studied. The position and form of precipitation lines depended primarily on the initial concentration of components and the degree of protein biotinylation. Free biotin, 1% SDS, and 6 M urea contained in the gel, as well as thermal denaturation of streptavidin inhibited the precipitate formation.