Catalytically perfect enzyme
Encyclopedia
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. kcat/Km factor of such enzyme is of order 108 to 109 M-1 s-1. Such reaction is 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.
Enzyme
Enzymes are proteins that catalyze chemical reactions. In enzymatic reactions, the molecules at the beginning of the process, called substrates, are converted into different molecules, called products. Almost all chemical reactions in a biological cell need enzymes in order to occur at rates...
that catalyzes so efficiently, that almost every time enzyme meets its substrate, the reaction occurs. kcat/Km factor of such enzyme is of order 108 to 109 M-1 s-1. Such reaction is only limited by substrate
Substrate (biochemistry)
In biochemistry, a substrate is a molecule upon which an enzyme acts. Enzymes catalyze chemical reactions involving the substrate. In the case of a single substrate, the substrate binds with the enzyme active site, and an enzyme-substrate complex is formed. The substrate is transformed into one or...
diffusion rate.
Some catalytically perfect enzymes are triose-phosphate isomerase
Triosephosphateisomerase
Triose-phosphate isomerase , is an enzyme that catalyzes the reversible interconversion of the triose phosphate isomers dihydroxyacetone phosphate and D-glyceraldehyde 3-phosphate....
, carbonic anhydrase
Carbonic anhydrase
The carbonic anhydrases form a family of enzymes that catalyze the rapid interconversion of carbon dioxide and water to bicarbonate and protons , a reversible reaction that occurs rather slowly in the absence of a catalyst...
, acetylcholinesterase
Acetylcholinesterase
"Acetylcholinesterase, also known as AChE or acetylcholine acetylhydrolase, is an enzyme that degrades the neurotransmitter acetylcholine, producing choline and an acetate group. It is mainly found at neuromuscular junctions and cholinergic nervous system, where its activity serves to terminate...
, catalase
Catalase
Catalase is a common enzyme found in nearly all living organisms that are exposed to oxygen, where it catalyzes the decomposition of hydrogen peroxide to water and oxygen...
, fumarase
Fumarase
Fumarase is an enzyme that catalyzes the reversible hydration/dehydration of Fumarate to malate. Fumarase comes in two forms: mitochondrial and cytosolic...
, β-lactamase
Beta-lactamase
Beta-lactamases are enzymes produced by some bacteria and are responsible for their resistance to beta-lactam antibiotics like penicillins, cephamycins, and carbapenems . These antibiotics have a common element in their molecular structure: a four-atom ring known as a beta-lactam...
, and superoxide dismutase
Superoxide dismutase
Superoxide dismutases are a class of enzymes that catalyze the dismutation of superoxide into oxygen and hydrogen peroxide. As such, they are an important antioxidant defense in nearly all cells exposed to oxygen...
.
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.