Rapid Sedimentation of Proteins through Starch

Abstract

PACKED potato starch, which has been widely used for zone electrophoresis, offers certain advantages when employed as a supporting medium in the ultracentrifuge. Boundaries are stabilized, making recovery of fractions easier, and the proteins thus far studied sediment at least twice as rapidly in starch as in free solution. This has been shown in experiments with rat hæmoglobin (1 per cent) or bovine serum albumin (1–5 per cent) stained with bromphenol blue centrifuged in starch and in free solution under identical conditions. Centrifugation was done in the ‘Spinco’ Model L centrifuge by use of an SW 391 swinging-bucket rotor at approximately 20°. A 0.1 ionic strength pH 7.5 phosphate–sodium chloride buffer was used in each instance. The ‘Lusteroid’ centrifuge tubes were completely filled with a slurry of starch–protein mixture and accelerated briefly to 20,000 r.p.m. After deceleration, excess fluid was removed and more starch slurry added. The packing procedure was repeated a second time and excess fluid again removed. It is important that the starch suspensions be freshly made, since part of the starch appears to dissolve slowly with time, destroying the effect observed here.