A catalytically perfect enzyme or kinetically perfect enzyme is an enzyme that catalyzes so efficiently, that almost every time enzyme meets its substrate, the reaction occurs. The specificity constant, kcat/Km, of such enzymes is on the order of 108 to 109 M-1 s-1, indicating high efficiency. Catalytically perfect reactions are only limited by substrate diffusion rate.
Some catalytically perfect enzymes are triose-phosphate isomerase, carbonic anhydrase, acetylcholinesterase, catalase, fumarase, β-lactamase, and superoxide dismutase.
Some enzymes operate with kinetics which are faster than diffusion rates, which would seem to be impossible. Several mechanisms have been invoked to explain this phenomenon. Some proteins are believed to accelerate catalysis by drawing their substrate in and preorienting them by using dipolar electric fields. Some invoke a quantum-mechanical tunneling explanation whereby a proton or an electron can tunnel through activation barriers, although proton tunneling remains a somewhat controversial idea.
Famous quotes containing the word perfect:
“Talk to every woman as if you loved her, and to every man as if he bored you, and at the end of your first season you will have the reputation of possessing the most perfect social tact.”
—Oscar Wilde (1854–1900)