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),(nu)over tilde>(as)(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. (C) 1994 Academic Press, Inc.