Catalytic mechanism of the aspartate proteinase pepsin A: An FTIR study

✍ Scribed by Georgios Iliadis; Georg Zundel; Bogumil Brzezinski

• Book ID: 101292600
• Publisher: John Wiley and Sons
• Year: 1997
• Tongue: English
• Weight: 208 KB
• Volume: 3
• Category: Article
• ISSN: 1075-4261
• DOI: 10.1002/(sici)1520-6343(1997)3:4<291::aid-bspy4>3.0.co;2-7

✦ Synopsis

The following FTIR difference spectra were studied: (pepsin) minus (Asp 215 or Asp 32 modified pepsin), (pepsin / pepstatin) minus (the modified pepsin / pepstatin), (at 40ЊC incubated pepsin / substrate) minus (pepsin / substrate at 4ЊC), and (at 40ЊC incubated pepsin / substrate) minus (EPNP modified pepsin / substrate). From these spectra, it is concluded that in native pepsin Asp 215 is protonated and Asp 32 deprotonated. A water molecule is present between these Asp residues. When substrate is added, Asp 215 is deprotonated and Asp 32 becomes protonated. This is performed by the hydrogen-bonded system Asp 215-water-Asp 32. This system shows very large proton polarizability due to collective proton motion. Asp 32 binds to the O atom of the peptide group. The catalytic mechanism is a base catalysis performed by the water molecule that is strongly polarized by the negatively charged Asp 215 residue. With their lone pairs, the water molecules attack the electrophilic carbon atom of the peptide group.