Study of the sodium dodecyl sulphate–protein complexes: evidence of their wormlike conformation by treating them as random coil polymers

The Kuhn statistical segment length, A, was determined for the sodium dodecyl sulphate (SDS)–protein complexes in two binding levels of SDS adsorbed onto the protein. These complexes are treated as random coil polymers. For the SDS–protein complex of binding level 1.4 g SDS per gram of protein, the value of A was found equal to 76 and 37 A in 0.01 and 0.1 M ionic strength, correspondingly. For the complex of binding level 0.4 g SDS per gram of protein, the value of A was found equal to 30 A. The calculation was based mainly on two equations (Eqs. 4 and 5; Dondos and Benoit, Polymer 18:1161, 1977; Dondos and Staikos, Colloid Polym Sci 273:623, 1995, correspondingly). Our findings are supported by gel permeation chromatography results, drawn according to the “modified universal calibration” and suggest that these complexes should be considered as wormlike polymers presenting a considerable draining effect.