Thermodynamic analysis of ionizable groups involved in the catalytic mechanism of human matrix metalloproteinase 7 (MMP-7)

► MMP-7 activity exhibits a broad bell-shaped pH-dependence with the pKe1 and pKe2 values of 4 and 10. ► The pKe2 value suggests Tyr or Lys, but no Lys is in the active site, and thus Tyr219 is the candidate. ► However, Tyr219 was declined to be the pKe2 residue by site-directed mutagenesis analysis of MMP-7. ► Thermodynamic analysis suggested that Glu198 is responsible for pKe1. ► It also suggested that a protein-bound water molecule is responsible pKe2.