Accessibility of tryptophan residues in immunoglobulin M as an index of its conformational changeability.

Demonstrated herein is the possibility of using the accessibility of tryptophan (Trp) residues in immunoglobulin M (IgM) upon modification with Koshland reagent (2-hydroxy-5-nitrobenzyl bromide) as an index of the conformational changeability of IgM. Of fourteen Trp's in the native IgM (per HL-region) only one appeared to be most accessible, evidently Trp312 in the mu-chain. Irreversible acidic and thermal conformational transitions in IgM increase the number of accessible Trp's approximately two-fold.

[Accessibility of tryptophan residues in immunoglobulin M molecule as an indicator of its conformational variability].

The accessibility of tryptophan residues in immunoglobulin M to modification with the Koshland reagent (2-hydroxy-5-nitrobenzyl bromide) was used as an indicator of its conformational variability. Of 14 tryptophan residues (per HL-fragment) in the native IgM, only one (presumably Trp312 in the mu-chain) was the most accessible. Irreversible acid- or temperature-induced conformational changes of IgM increased almost 2-fold the number of accessible tryptophan residues.

[Study of the structure of immunoglobins by small-angle x-ray diffraction. I. The structure of IgMCep in solution].

The data of small-angle X-ray scattering from monoclonal immunoglobulin MCep (IgM) enabled the shape and geometrical parameters of the molecule in solution at 23 degrees C to be established. The molecule is a flat, strongly anisometric particle with radius of gyration 115 A, volume 1,8 X 10(6) A3, maximum size 380 A, thickness 35-40 A. The most probable molecular model in the approximation of homogeneous electron density in the molecule was suggested, its geometry fitting the experimental parameters.