Superefficient enzymes.
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.
Stroppolo
M E
ME
INFM and Department of Biology, University of Rome Tor Vergata, Rome, Italy.
Falconi
M
M
Caccuri
A M
AM
Desideri
A
A
D000818:Animals; D001665:Binding Sites; D002384:Catalysis; D004058:Diffusion; D004798:Enzymes / Q000737:chemistry*; D007700:Kinetics; D008956:Models, Chemical; D008958:Models, Molecular; D011485:Protein Binding; D055672:Static Electricity; D013379:Substrate Specificity; D013482:Superoxide Dismutase / Q000737:chemistry; D013997:Time Factors; D014305:Triose-Phosphate Isomerase / Q000737:chemistry
D004798:Enzymes; D013482:Superoxide Dismutase; D014305:Triose-Phosphate Isomerase