[Effect of perturbing agents on the dynamic properties of immunoglobulin fragments]

The effect of NaCl, (NH4)2SO4, sodium dodecylsulphate and temperature on conformational properties of light-chain dimers and the Fab-fragments of immunoglobulins G has been investigated using the spin-label method. All these agents despite their different nature, induce qualitatively the same shift in the equilibrium between the A- and B-states of spin label towards the state of higher microviscosity A. The effect of 1.2 M NaCl and 0.75 M (NH4)2SO4 increase the stability of IgG in relation to temperature, as a result of this shift. The data obtained are interpreted in terms of the dynamic model of protein behaviour in water suggested earlier. In accordance with the model the action of the agents perturbing the conformation of protein and the ordered structure of water in the non-polar cavities of protein, reduce the life-time of this cavities in the water accessible state.