title: Unusual solvent isotope effects on the aminoacylase-catalyzed hydrolysis of acetylamino acids.
abstract: 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 (kcat(D)/kcat(H) = 0.7 at pH 6), virtually absent at neutrality, and distinctly inverse (kcat(D)/kcat(H) = 1.4) at pH 9. Km was not significantly affected. The rates of Ac-L-Phe hydrolysis in D2O considerably exceeded those in H2O at any pH between 6.5 and 9. We explain this unusual effect of D2O on aminoacylase I catalysis by an inverse equilibrium effect partially cancelling or, at high pH, reversing a normal isotope effect on kcat.
mesh_terms: D000581:Amidohydrolases / Q000378:metabolism*; D000596:Amino Acids / Q000378:metabolism*; D000818:Animals; D002384:Catalysis; D003903:Deuterium; D006863:Hydrogen-Ion Concentration; D006868:Hydrolysis; D007668:Kidney / Q000201:enzymology; D007700:Kinetics; D012997:Solvents; D013552:Swine
chemical_list: D000596:Amino Acids; D012997:Solvents; D003903:Deuterium; D000581:Amidohydrolases; C019672:aminoacylase I