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:
“There was an artist in the city of Kouroo who was disposed to strive after perfection. One day it came into his mind to make a staff. Having considered that in an imperfect work time is an ingredient, but into a perfect work time does not enter, he said to himself, It shall be perfect in all respects, though I should do nothing else in my life.”
—Henry David Thoreau (1817–1862)