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A comparative study of the conformational and dynamics properties of the ACTH-like linear peptides, sequences of which correspond to amino acid residues 11-20 of the heavy chain of human immunoglobulin G1 Eu, residues 78-85 of human pro-interleukin-1 alpha and site 10-18 of human ACTH, was performed in aqueous solution and dimethylsulfoxide by 1H-NMR spectroscopy at 400 MHz. The peptides were shown to possess an unordered unfolded flexible conformation in aqueous solution. The revealed structural and dynamic features of the peptides are discussed together with biological activity of this class of compounds.

The evidence of the intramolecular flexibility of human myeloma immunoglobulin G belonging to the second, third and fourth subclasses has been obtained using the impulse NMR method. It has been found that the degree of intramolecular flexibility for the myeloma immunoglobulin G belonging to the first subclass decreases significantly by cooling from 37 to 10 degrees.

A high degree of correlation between the capability of subclasses of human immunoglobulins G to form aggregates due to thermal treatment, and their complement-binding activity was established. On the basis of the experimental data obtained by the methods of light scattering, circular dichroism, microcalorimetry, it was supposed that "hinge" region of immunoglobulins G participates in the initial stage of thermal aggregation and in the activation of the process of complement binding.

Using the methods of difference adiabatic scanning microcalorimetry and difference thermal perturbation spectrophotometry it was established that both the Fc subunits within the intact immunoglobulins G of different subclasses, and the Fc fragments corresponding to them significantly differ in conformational properties. These differences are associated with a different energy of interactions between the CH2 and CH3 domains and also with a different rigidity of structure of the N- and C-terminal parts of the CH2 domains. The analysis of these data allowed to suggest that the "hinge region" interacts with the CH2 domains and the difference in the structure of this region affect the conformation of the Fc subunits. Possible models of the "hinge regions" in immunoglobulins G of the first, second and fourth subclasses, and also their arrangement relative to the CH2 domains were proposed. The analysis of curves of the small-angle scattering of X-rays shows an agreement between the theoretical models and experimental data.