Aspartic proteinases--Fourier transform IR studies of the aspartic carboxylic groups in the active site of pepsin.
Fourier transform (FTIR) difference spectra of pepsin minus diazoacetylnorleucine methyl ester (DAN) or minus diazoacetyl-L-phenylalanine methyl ester (DAP) modified pepsin, respectively, demonstrated that Asp-215 is not deprotonated in pepsin. The FTIR difference spectrum of pepsin minus 1,2-epoxyparanitrophenoxypropane (EPNP) modified pepsin demonstrates that Asp-32 is present in pepsin as CO2- anion. The position of the v(C = O) vibration demonstrates that no (O...H...O)- hydrogen bond between Asp-215 and Asp-32 is formed. Furthermore, no H3O+ is present in the active center. Studies of the complex of pepsin with the inhibitor pepstatin prove that the inhibitor removes the water from the active site and Asp-32 becomes protonated.
Iliadis
G
G
Institute of Physical Chemistry, University of Munich, Germany.
Zundel
G
G
Brzezinski
B
B
D001224:Aspartic Acid; D016282:Aspartic Acid Endopeptidases / Q000737:chemistry*; D001665:Binding Sites; D006860:Hydrogen Bonding; D009646:Norleucine / Q000031:analogs & derivatives; D010434:Pepsin A / Q000737:chemistry*; D010649:Phenylalanine / Q000031:analogs & derivatives; D011487:Protein Conformation; D017550:Spectroscopy, Fourier Transform Infrared / Q000379:methods
C089752:diazoacetylphenylalanine methyl ester; D001224:Aspartic Acid; D010649:Phenylalanine; C000909:N-diazoacetylnorleucine methyl ester; D009646:Norleucine; D016282:Aspartic Acid Endopeptidases; D010434:Pepsin A