The distribution of protein and enzyme activities in membrane fractions obtained from pea seedlings. A microsomal membrane fraction was fractionated by a 10-step aqueous polymer two-phase counter current distribution and the resulting 10 membrane fractions analyzed. A, The normalized activities of choline phosphotransferase for ER (solid triangles; 100 corresponds to 10 pmol·[mg protein]-1·min-1), cytochrome C oxidase for mitochondrial inner membrane (open triangles; 100 corresponds to 1.46 mmol·[mg protein]-1·min-1) and 1,3-β-glucan synthase for plasma membrane (solid squares; 100 corresponds to 0.53 μmol·[mg protein]-1·min-1). The dashed line shows the normalized protein distribution between the fractions. B, The normalized chlorophyll content of thylakoid (open squares; 100 corresponds to 0.12 mg·[mg protein]-1), the normalized binding of a monoclonal anti-β-COP anti body for Golgi (solid circles; antibody binding only occurred to fractions 2–4, 100 corresponds to the highest binding), 1,3-β-glucan synthase for plasma membrane (solid squares; 100 corresponds to 0.43 μmol·[mg protein]-1·min-1). and the normalized distribution of protein between the fractions (dashed line). As all parameters could not be assayed on the fractions from a single 10-step membrane distribution, the panels A and B present the results from two independent experiments, with the plasma membrane marker and the protein distribution analyzed for both.