Superefficient enzymes

Abstract

Diffusion-controlled enzymes are characterized by second-order rate constants in the range 10(8)-10(10) M(-1)s(-1). These values are at the upper end of the observed rates of many enzyme-substrate reactions and have been predicted by theoretical studies on bimolecular reaction in solution. Such enzymes are considered to be perfect, since their rate-limiting step is not due to any chemical event but to the diffusional association rate between the enzyme and the substrate. Often the enzyme-substrate encounter is facilitated either through the presence of a strong attractive electric field, produced by charges on the enzyme surface, or through the reduction in the dimension of the search process. Here we provide a brief review of some of the enzymes characterized by a very fast second-order constant, focusing attention on triose phosphate isomerase and Cu,Zn superoxide dismutase taken as typical examples of such highly tuned enzymes.

Triosephosphate Isomerases in Italian Ryegrass (Lolium multiflorum): Characterization and Susceptibility to Herbicides

“…A high degree of analogy is evident, which is in strong accordance with the same catalytic role of these enzymes (1)(2)(3). According to the current model, His-96 and Asn-10 should be involved in stabilizing and polarizing the substrate by forming hydrogen bonds; Glu-166 serves to generate an intermediate of reaction for the final enolization, and Lys-12 should be involved in binding of substrate and catalysis (1,3,48). The three amino acid residues, Cys-13, -67, and -127, are considered to participate in regulation of TPI by (Figure 4 A) 16.1 177.10 93.9 fraction with the highest TPI specific activity (second chromatography, Figure 4 B S-glutathionylation, although Cys-67 is not present in pTPI (1,2,49).…”

Three-dimensional structure of a halotolerant algal carbonic anhydrase predicts halotolerance of a mammalian homolog

“…The electrostatic interactions considered here could be partly akin to mechanisms proposed for modulation of enzymatic activity by ''steering'' of substrates toward the active site (41)(42)(43) or modification of interaction potentials within the active site (44).…”

In silico prediction of the effects of mutations in the human triose phosphate isomerase gene: Towards a predictive framework for TPI deficiency

“…TPI is an example of a 'kinetically perfect' enzyme since its activity is limited only by the rates of diffusion of substrate and product molecules (Stroppolo et al, 2001). In humans, TPI is encoded by a single gene (TPI1) located at chromosome 12p13 and is expressed in all tissues.…”