Skip to main content
. 2004 Oct 26;383(Pt 3):551–559. doi: 10.1042/BJ20040054

Figure 6. pH-dependence of (a) kcat/Km and (b) kcat for S. aureus DNA-ligase-catalysed ligation of the AE-labelled DNA substrate.

Figure 6

These studies were carried out in the following assay buffers at room temperature: sodium acetate (pH 5.2 and 5.6), Hepes (pH 6.0, 6.5, 7.1 and 7.4) and Tris/HCl (pH 8.0). Reactions were initiated by the addition of enzyme (50 pM final enzyme concentration) to solutions of buffer containing substrate (2–10 nM). The points are experimental and the lines are theoretical for the single ionization equation k=k~/(1+[H+]/Ka), where k=kcat or k=kcat/Km and k~=k~cat or k~cat/K~m (pH-independent kinetic parameters) (a) pKa=7.1±0.1, k~cat/K~m=(4.1±0.1)× 105 M−1·s−1 and (b) pKa=6.6±0.1, k~cat=0.009±0.001 s−1.