Rate‐determining steps in penicillopepsin‐catalysed reactions

FEBS Letters

Hofmann, Theo¹  Cunningham, Annie¹  Hofmann, Martin I.² 

[1] Departments of Biochemistry, University of Toronto, Toronto, M5S 1A8 Canada;Departments of Zoology, University of Toronto, Toronto, M5S 1A8 Canada

关键词: Penicillopepsin;    Aspartic proteinase;    Enzyme kinetics;    Enzyme mechanism;    Ac-;    acetyl;    FAB;    fast atom bombardment;    HPLC;    high-pressure liquid chromatography;    Nph;    p-nitrophenylalanyl;    OMe;    O-methyl ester;    TFA;    trifluoroacetic acid;    the definition of Schechter and Berger [1] for denoting amino acid residues in peptide substrates as P1 to P nand P1' to P n ' and subsites in the enzyme to which the side chains of these residues bind as S1 to S n ' and S1' to S n ';    respectively;    is used throughout;   

DOI  :  10.1016/0014-5793(90)80522-K

学科分类：生物化学/生物物理

来源: John Wiley & Sons Ltd.

【 摘 要 】

The hydrolysis of Ac-(Ala)₂-Lys-Nph-(Ala)₂-amide (II) by penicillopepsin is characterized by a solvent isotope effect of 2.11, whereas the hydrolysis of Ac-Lys-Nph-amide (I) shows no solvent isotope effect. The dependence of the isotope effect on the concentration of D₂O in H₂O for substrate II is not linear and suggests that two or more protons are involved in its rate-determining step. We propose that for substrate I the rate-determining step is the distortion of the scissile bond towards a tetrahedral configuration, and for substrate II a conformational change induced by the occupation of the S₃ pocket in the enzyme.

【 授权许可】

Unknown