Fig. 4.

Effects of exo-neuraminidase addition on NMR spectra, monitored through the peak height of the ¹³CH-3 signals. (A) Region corresponding to ¹³CH-3 signals from ¹H-¹³C HSQC spectra of EV239^+neuS cells with ¹³C,¹⁵N-PSA before addition of the enzyme and at two representative times (indicated in the figure) after addition. The signals from PSA (labeled p) decrease in intensity as the monomer (m) increases. (B) Plot of the signal intensities from m3_eq (■) and p3_eq (●) as function of time after enzyme addition. Data fitting to single exponential functions (solid line) yielded identical rate constants (0.27 ± 0.01 h⁻¹) with opposite sign.