Contribution of a low-barrier hydrogen bond to catalysis is not significant in ketosteroid isomerase.

ABSTRACT: Low-barrier hydrogen bonds (LBHBs) have been proposed to have important influences on the enormous reaction rate increases achieved by many enzymes. Δ(5)-3-ketosteroid isomerase (KSI) catalyzes the allylic isomerization of Δ(5)-3-ketosteroid to its conjugated Δ(4)-isomers at a rate that approaches the diffusion limit. Tyr14, a catalytic residue of KSI, has been hypothesized to form an LBHB with the oxyanion of a dienolate steroid intermediate generated during the catalysis. The unusual chemical shift of a proton at 16.8 ppm in the nuclear magnetic resonance spectrum has been attributed to an LBHB between Tyr14 Oη and C3-O of equilenin, an intermediate analogue, in the active site of D38N KSI. This shift in the spectrum was not observed in Y30F/Y55F/D38N and Y30F/Y55F/Y115F/D38N mutant KSIs

SUBMITTER: Jang DS 

PROVIDER: S-EPMC4443282 | biostudies-literature | 2015 May

REPOSITORIES: biostudies-literature