CHANGES IN THE PHYSICOCHEMICAL PROPERTIES OF THE DETERGENT OCTYL GLUCOSIDE DURING MEMBRANE-PROTEIN CRYSTALLIZATION USING A SALT AS THE PRECIPITANT

In membrane protein crystallization experiments, numerous changes can occur to the physico-chemical properties of a detergent during vapor equilibration of an aqueous protein solution when the precipitant is a salt. The effect of salts on the behavior of the non-ionic detergent octyl-beta-D-glucopyranoside was investigated. The increase in salt concentration caused a salt dependent decrease in the critical micellization concentration. Simultaneously, for a given temperature, the occurrence of a clouding phenomenon resulted in phase separation. In the presence of ammonium sulfate the hydrodynamic radius of the micellar particles was significantly increased. The use of the detergent concentration as a variable for the crystallization of membrane proteins is discussed in the light of results obtained with bacteriorhodopsin.