Kinetic perfection
Encyclopedia
Kinetic perfection, also known as catalytic perfection, refers to enzyme
s that are diffusion-limited; that is, the reaction they catalyze occurs as quickly as the reactants diffuse to the enzyme. The time needed for the reaction to occur is negligible compared to the time it takes for the substrate to enter, and product to leave, the active site
.
Kinetic perfection: "Their [the enzymes] catalytic velocity is restricted only by the rate at which they [the enzymes] encounter substrates in a solution."
This means that the rate of the enzyme catalysed reaction is actually limited by diffusion
. The enzyme 'processes' the substrate
well before it encounters another molecule. An example of a kinetically perfect enzyme is Triose phosphate isomerase, which is involved in the glycolytic pathway.
Some kinetically perfect enzymes may employ the 'Circe Effect', the use of electostatic forces to attract substrate molecules into active sites.
It is worth noting that there are not many kinetically perfect enzymes. This can be explained in terms of natural selection
. An increase in catalytic speed may be favoured as it could confer some advantage to the organism. However, when the catalytic speed outstrips diffusion speed (i.e. substrates entering and leaving the active site, and also encountering susbstrates) there is no more advantage to increase the speed even further. Increasing the catalytic speed past the diffusion speed will not aid the organism in any way. Therefore these perfect enzymes must have come about by 'lucky' random mutation
which happened to spread, or because the faster speed was once useful as part of a different reaction in the enzyme's ancestry.
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...
s that are diffusion-limited; that is, the reaction they catalyze occurs as quickly as the reactants diffuse to the enzyme. The time needed for the reaction to occur is negligible compared to the time it takes for the substrate to enter, and product to leave, the active site
Active site
In biology the active site is part of an enzyme where substrates bind and undergo a chemical reaction. The majority of enzymes are proteins but RNA enzymes called ribozymes also exist. The active site of an enzyme is usually found in a cleft or pocket that is lined by amino acid residues that...
.
Kinetic perfection: "Their [the enzymes] catalytic velocity is restricted only by the rate at which they [the enzymes] encounter substrates in a solution."
This means that the rate of the enzyme catalysed reaction is actually limited by diffusion
Diffusion
Molecular diffusion, often called simply diffusion, is the thermal motion of all particles at temperatures above absolute zero. The rate of this movement is a function of temperature, viscosity of the fluid and the size of the particles...
. The enzyme 'processes' the 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...
well before it encounters another molecule. An example of a kinetically perfect enzyme is Triose phosphate isomerase, which is involved in the glycolytic pathway.
Some kinetically perfect enzymes may employ the 'Circe Effect', the use of electostatic forces to attract substrate molecules into active sites.
It is worth noting that there are not many kinetically perfect enzymes. This can be explained in terms of natural selection
Natural selection
Natural selection is the nonrandom process by which biologic traits become either more or less common in a population as a function of differential reproduction of their bearers. It is a key mechanism of evolution....
. An increase in catalytic speed may be favoured as it could confer some advantage to the organism. However, when the catalytic speed outstrips diffusion speed (i.e. substrates entering and leaving the active site, and also encountering susbstrates) there is no more advantage to increase the speed even further. Increasing the catalytic speed past the diffusion speed will not aid the organism in any way. Therefore these perfect enzymes must have come about by 'lucky' random mutation
Mutation
In molecular biology and genetics, mutations are changes in a genomic sequence: the DNA sequence of a cell's genome or the DNA or RNA sequence of a virus. They can be defined as sudden and spontaneous changes in the cell. Mutations are caused by radiation, viruses, transposons and mutagenic...
which happened to spread, or because the faster speed was once useful as part of a different reaction in the enzyme's ancestry.