Inverse enzyme isotope effects in human purine nucleoside phosphorylase with heavy asparagine labels.

ABSTRACT: Transition path-sampling calculations with several enzymes have indicated that local catalytic site femtosecond motions are linked to transition state barrier crossing. Experimentally, femtosecond motions can be perturbed by labeling the protein with amino acids containing ¹³C, ¹⁵N, and nonexchangeable ²H. A slowed chemical step at the catalytic site with variable effects on steady-state kinetics is usually observed for heavy enzymes. Heavy human purine nucleoside phosphorylase (PNP) is slowed significantly (k_chemlight/k_chemheavy = 1.36). An asparagine (Asn243) at the catalytic site is involved in purine leaving-group activation in the PNP catalytic mechanism. In a PNP produced with isotopically heav

SUBMITTER: Harijan RK 

PROVIDER: S-EPMC6142206 | biostudies-literature | 2018 Jul

REPOSITORIES: biostudies-literature