Quantitative analysis of residual detergent in proteoliposomes by Fourier transform infrared spectroscopy.

An infrared spectroscopic method has been developed to quantify the residual amount of detergent present in membranes, e.g., after reconstitution of a membrane protein in phospholipids. A detergent-specific band is selected in the ir spectrum and the intensity is ratioed against a phospholipid-specific band (around 1235 cm-1, vas (P = O)). This ratio shows a linear relation with the molar ratio of detergent of phospholipid, down to as low as 1 to 10. The new method is illustrated in two case studies, viz., tris(hydroxyethyl)ammonium cholate in Na+/K(+)-ATPase proteoliposomes and n-dodecyl-beta-D-maltoside in rhodopsin proteoliposomes.