Fig. 2.
Sedimentation equilibrium. Samples contained 2.5 μM enzyme ((a) wt SfiI; (b) Y68F) and 2.5 μM DNA (HEX-21) in AUC buffer at 20 °C. The two main panels show the differences in absorbance at 539 nm between sample and reference channels as a function of centrifugal radius, after centrifugation for 16 h at 10,000 rpm at 20 °C. The red lines through the experimental points correspond to the best global fit of the data at varied speeds to the equation for a single species.49 The best fits to the data for the complexes of HEX-21 with wt SfiI (a) and with Y68F (b) gave Mr values of 154,203 and 156,274, respectively. The upper panels show the distribution of the residuals between data and optimal fits.