Microanalytical partition of rat-liver homogenates by poly(ethylene glycol)-dextran counter-current distribution.

1. The principal organelles from rat liver homogenates were fractionated by counter-current partition between solutions of dextran T50 and poly(ethylene glycol) 6000 in 0.25 M sucrose containing 10 mM sodium phosphate/phosphoric acid buffer, pH 7.4. 2. A small-volume (1.3-ml sample well)counter-current partition apparatus capable of 17 transfers, in which separation of the phases was enhanced by low-speed centrifugation, was used. 3. Variations in distribution of organelles was observed with increasing concentration of dextran and/or poly(ethylene glycol). At a constant polymer composition of 5.0% (w/w) dextran and 4.0% (w/w) poly(ethylene glycol), increasing concentrations of sodium chloride (2.5 mM, 5 mM and 10 mM) also altered the partition of the organelles. 4. Useful analytical resolution of the various organelles was achieved. In particular, separation of endoplasmic reticulum from plasma membrane components was obtained.