Advantages of the fixed-angle rotor for the separation of density-labelled from unlabelled proteins by isopycnic equilibrium centrifugation.

A comparison has been made between the swinging-buckets rotor and the fixed-angle rotor for density-labelling experiments. The enzymes examined were beta-galactosidase (beta-D-galactoside galactohydrolase, EC 3.2.1.23), L-phenylalanine ammonia-lyase (EC 4.3.1.5) and acid phosphatase (orthophosphoric monoester phosphohydrolase, EC 3.1.3.2); it was found that the fixed-angle rotor offered greater separation and resolution and shorter equilibration times compared with the swinging-buckets rotor at the same angular velocity. By exploiting the greater flexibility offered by the fixed-angle rotor it is possible to obtain either a 6-fold improvement in separation or a 6-fold reduction in equilibration time. The significance of these results for density-labelling work is discussed.