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Ultraviolet-visible spectroscopy has been used to follow the solubilization of the dark-adapted purple membrane of Halobacterium halobium by Triton X-100. Turbidity of purple membrane fragments and absorbance of bacteriorhodopsin variations during continuous addition of detergent give solubilization profiles exhibiting several break points corresponding to different equilibrium stages of the solubilization process. The present method allows the determination of the detergent to protein+lipid ratio in mixed aggregates at the corresponding break points. It was concluded that, when performed systematically, this technique is a very convenient and powerful tool for the quantitative study of biomembrane-to-micelle transition.

Reconstituted vesicular stomatitis virus (VSV) envelopes were formed by solubilization of the viral envelope with Triton X-100 followed by removal of detergent by direct addition of SM2 biobeads. We provide direct demonstration of fusion of reconstituted VSV with cells using fluorescent lipid and aqueous probes incorporated into the VSV virosomes during reconstitution. We show a direct comparison of the kinetics and pH profile of fusion with cells between reconstituted VSV and fluorescently labeled intact virus. With this preparation it is now possible to gain additional information about the role of cooperativity in viral protein-mediated fusion, and to permit construction of efficient vehicles for delivery of drugs and other materials into cells.