Catalytically perfect enzyme
A catalytically perfect enzyme or kinetically perfect enzyme is an enzyme that catalyzes so efficiently that in almost every encounter between enzyme and substrate corresponding runs a catalytic reaction. The kcat / Km factor of such an enzyme is of the order 108 to 109 M-1 s -1. Thus, the reaction of the substrate and enzyme is limited only by the rate of diffusion.
Examples of catalytically perfect enzymes are, for example, triose phosphate isomerase, carbonic anhydrase, acetylcholinesterase, catalase, fumarase, β -lactamase, and superoxide dismutase.
Some enzymes, however, show a rate that is faster than the diffusion rate, which seems impossible at first glance. To explain this phenomenon, various mechanisms have been proposed:
Some enzymes are believed to accelerate catalysis by itself " use " their substrates and align them with electric fields. Another theory proposes a quantum mechanical approach before, a proton or an electron can pass through a potential barrier by means of the tunnel effect, however, this approach is considered inconsistent, at least for protons. However, a tunnel effect for protons at tryptamine was observed. Due to this fact, the suspicion arises, the process of enzyme catalysis could be better described, assuming the passage by a potential hurdle in the traditional model, a substrate must exceed a certain activation energy to leave its potential well.