Comparative investigations of the molecular properties of detergents and protein-detergent complexes

Investigations of monomeric and micellar detergents, protein-detergent comp lexes, as well as native and denatured proteins by means of various physico chemical techniques yield a wide range of molecular characteristics of the components under analysis. Varying the experimental conditions (e.g., the c oncentration of solutes or the ionic strength of the medium) allows the mas s, gross structure, and structural details of the macromolecular components to be determined. However, several modifications of the conventional techn iques and evaluation procedures have to be applied in order to analyze mult icomponent systems consisting of several low-molecular, micellar, and macro molecular components in an appropriate way. In the case of weakly absorbing detergents, labeling of the detergent micelles by specific dyes is require d. Evidently, impurities and lack of homogeneity of many detergents may sev erely disturb the precise evaluation of the experiments; both necessitate a series of precautions in order to avoid misinterpretations. Analytical ult ra-centrifugation, size-exclusion chromatography, together with viscometry and densimetry, yield molar masses, mass distributions, and the overall str ucture of micellar and macromolecular molecules. In contrast, spectroscopic methods (UV absorption, fluorescence emission and excitation, far- and nea r-UV circular dichroism) monitor only local details of detergent-induced ch anges in the environment of aromatic residues. The technique of sodium dode cyl sulfate-polyacrylamide gel electrophoresis is routinely applied in bioc hemical work in order to establish molar masses of simple and conjugated pr oteins. To study the binding behavior of detergents to proteins in quantita tive terms, however, techniques (e.g., equilibrium centrifugation, electrop horesis and chromatography) involving detergent concentrations have to be u sed.