Urease activity and l-ascorbic acid

Figures & data

Scheme 1.  Oxidation of L-ascorbic acid

Figure 1.  Time courses of urease inactivation (semilogarithmic plots of residual activity (RA) versus incubation time) by: (A) AA in unbuffered system, and (B) acetate buffer. The RA values are reported as percent of the control activity.

Figure 2.  Dose-response curves for 20 min incubation observed in: (A) AA unbuffered solutions, and (B) acetate buffer.

Figure 3.  Time courses of urease inactivation (residual activity (RA) versus incubation time) by 10 mM AA and DHA in buffered system (200 mM phosphate buffer pH 7.2) in the absence and presence of 10 μM Fe³⁺ ions. The RA values are reported as percent of the control activity.

Figure 4.  Representative UV-vis spectra of: (A) AA, and (B) DHA during their conversions in 200 mM phosphate buffer pH 7.2, 1 mM EDTA. The insets present kinetic curves of the change in absorbance at 265 nm over time.

Figure 5.  Urease inactivation by 10 mM DHA in the presence of 10 μM Fe³⁺ in 200 mM phosphate buffer at pHs in the range 6.2–8.2; (A) time courses RA versus time, and (B) semi-logarithmic plots of RA versus time. The RA values are reported as percent of the control activity.

Figure 6.  Effect of pH on rate constant of urease inactivation by 10 mM DHA in the presence of 10 μM Fe³⁺ ions.

Figure 7.  Kinetic curves of DHA decomposition in the presence of Fe³⁺ ions at different pHs in the range 6.2–8.2: (A) change in absorbance at 265 nm (27°C), and (B) change in pH in 20 mM phosphate buffer.

Figure 8.  Protection of urease by catalase (grey) and SOD (black) against inactivation by DHA-Fe³⁺.

Figure 9.  Reactivation of (DHA-Fe³⁺)-inhibited urease by DTT (pH 8.2).