Inelastic laser light scattering and particle size of detergent-treated microsomes

Using inelastic laser light scattering we have determined the hydrodynamic diameters of a variety of hepatic microsomal preparations. Whole microsomes have a diameter of 3200 Å. Treatment of microsomes with deoxycholate or cholate and chromatography on DEAE-cellulose give three protein fractions: a “non-absorbed” fraction with particles 2650 Å in diameter, cytochrome P-420 1700 Å in diameter and cytochrome c reductase 760 Å in diameter. Preparation of cytochrome P-450 by (NH₄)₂SO₄ precipitation from cholate solution gives particles 640 Å in diameter. All of these sizes are much too large to represent single molecular species, indicating that these fractions are aggregates of membrane proteins with varying concentrations of lipids.