Elution countercurrent distribution.
The single withdrawal technique, here called elution countercurrent distribution, was applied for the first time on aqueous two-phase systems. The modifications necessary for elution countercurrent distribution of a thin-layer countercurrent distribution apparatus are described. The results from a test run with sulfuric acid showed good agreement between the experimental and the theoretical curves for elution countercurrent distribution. Thylakoid membrane vesicles from spinach chloroplasts were subjected to the elution countercurrent distribution. A gradient of NaCl in the eluting upper phase was used to elute the different fractions in order of their affinity for the moving upper phase. Inside-out thylakoid vesicles were resolved into two major and several minor fractions having different chlorophyll a/b ratios. Sonicated inside-out thylacoid vesicles were resolved into at least five different fractions with different chlorophyll a/b ratios. An increased resolution is obtained with elution countercurrent distribution compared to the fundamental process.