FIG. 5.

Effect of pH on sialidase activity, determined by using the fluorescent substrate 4MU-Neu5Ac. (A) Crude recombinant sialidase preparations from E. coli DH5α (□, pNEU101 [nanH]; ▵, pAH502 [nanB]) and purified recombinant NanH (○). (B) Activity of two wild-type P. multocida isolates, 86-1913 (◊) and X-73 (▿). The rates of release of 4-methylumbelliferone (4-MU) from the substrate were measured fluorometrically. The buffers used were citrate-phosphate (pH 3.1 to 7.1), Tris-HCl (pH 7.6 to 8.9), and glycine-NaOH (pH 9.5 to 10.5). Equal amounts of activity were used for each assay. Each reaction was done in triplicate, results are plotted as means ± standard deviations.