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Unusual solvent isotope effects on the aminoacylase‐catalyzed hydrolysis of acetylamino acids
Author(s) -
Henseling Johannes,
Röhm Klaus-Heinrich
Publication year - 1987
Publication title -
febs letters
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.593
H-Index - 257
eISSN - 1873-3468
pISSN - 0014-5793
DOI - 10.1016/0014-5793(87)81184-5
Subject(s) - enzyme kinetics , chemistry , kinetic isotope effect , hydrolysis , catalysis , solvent , substrate (aquarium) , kinetics , medicinal chemistry , stereochemistry , deuterium , active site , organic chemistry , biology , physics , quantum mechanics , ecology
The deuterium solvent isotope effect on hydrolysis of acetylamino acids catalyzed by porcine kidney aminoacylase I (EC 3.5.1.14) was studied. With Ac‐L‐Met, a ‘standard’ aminoacylase substrate, the effect was normal at low pH ( k cat(D) / k cat(H) = 0.7 at pH 6), virtually absent at neutrality, and distinctly inverse ( k cat(D) / K cat(H) = 1.4) at pH 9. K m was not significantly affected. The rates of Ac‐L‐Phe hydrolysis in D 2 O considerably exceeded those in H 2 O at any pH between 6.5 and 9. We explain this unusual effect of D 2 O on aminoacylase I catalysis by an inverse equilibrium effect partially cancelling or, at high pH, reversing a normal isotope effect on k cat .