Committed step
Encyclopedia
In enzymology, the committed step (also known as the first committed step) is an effectively irreversible
enzymatic reaction
that occurs at a branch point during the biosynthesis of some molecules.
and will ultimately end up in the pathway's final product. The first committed step should not be confused with the rate-determining step
, which is the slowest step in a reaction or pathway. However, it is sometimes the case that the first committed step is in fact the rate-determining step as well.
. Such regulation ensures that pathway intermediates
do not accumulate, a situation that can be wasteful or even harmful to the cell.
Irreversibility
In science, a process that is not reversible is called irreversible. This concept arises most frequently in thermodynamics, as applied to processes....
enzymatic reaction
Enzyme catalysis
Enzyme catalysis is the catalysis of chemical reactions by specialized proteins known as enzymes. Catalysis of biochemical reactions in the cell is vital due to the very low reaction rates of the uncatalysed reactions....
that occurs at a branch point during the biosynthesis of some molecules.
What it means
As the name implies, after this step, the molecules are "committed" to the pathwayMetabolic pathway
In biochemistry, metabolic pathways are series of chemical reactions occurring within a cell. In each pathway, a principal chemical is modified by a series of chemical reactions. Enzymes catalyze these reactions, and often require dietary minerals, vitamins, and other cofactors in order to function...
and will ultimately end up in the pathway's final product. The first committed step should not be confused with the rate-determining step
Rate-determining step
The rate-determining step is a chemistry term for the slowest step in a chemical reaction. The rate-determining step is often compared to the neck of a funnel; the rate at which water flows through the funnel is determined by the width of the neck, not by the speed at which water is poured in. In...
, which is the slowest step in a reaction or pathway. However, it is sometimes the case that the first committed step is in fact the rate-determining step as well.
Regulation
Metabolic pathways require tight regulation so that the proper compounds get produced in the proper amounts. Often, the first committed step is regulated by processes such as feedback inhibition and activationActivation
Activation in chemical sciences generally refers to the process whereby something is prepared or excited for a subsequent reaction.- Chemistry :...
. Such regulation ensures that pathway intermediates
Reaction intermediate
A reaction intermediate or an intermediate is a molecular entity that is formed from the reactants and reacts further to give the directly observed products of a chemical reaction. Most chemical reactions are stepwise, that is they take more than one elementary step to complete...
do not accumulate, a situation that can be wasteful or even harmful to the cell.
Examples of enzymes that catalyze the first committed steps of metabolic pathways
- Phosphofructokinase 1 catalyzes the first committed step of glycolysisGlycolysisGlycolysis is the metabolic pathway that converts glucose C6H12O6, into pyruvate, CH3COCOO− + H+...
. - LpxC catalyzes the first committed step of lipid ALipid ALipid A is a lipid component of an endotoxin held responsible for toxicity of Gram-negative bacteria. It is the innermost of the three regions of the lipopolysaccharide molecule, and its hydrophobic nature allows it to anchor the LPS to the outer membrane...
biosynthesis. - 8-amino-7-oxononanoate synthase8-amino-7-oxononanoate synthaseIn enzymology, a 8-amino-7-oxononanoate synthase is an enzyme that catalyzes the chemical reactionThus, the two substrates of this enzyme are 6-carboxyhexanoyl-CoA and L-alanine, whereas its 3 products are 8-amino-7-oxononanoate, CoA, and CO2....
catalyzes the first committed step in plant biotinBiotinBiotin, also known as Vitamin H or Coenzyme R, is a water-soluble B-complex vitamin discovered by Bateman in 1916. It is composed of a ureido ring fused with a tetrahydrothiophene ring. A valeric acid substituent is attached to one of the carbon atoms of the tetrahydrothiophene ring...
synthesis. - MurA catalyzes the first committed step of peptidoglycanPeptidoglycanPeptidoglycan, also known as murein, is a polymer consisting of sugars and amino acids that forms a mesh-like layer outside the plasma membrane of bacteria , forming the cell wall. The sugar component consists of alternating residues of β- linked N-acetylglucosamine and N-acetylmuramic acid...
biosynthesis.
Other uses
The term has also been applied to other processes that involve a series of steps. For example, the binding of egg and sperm can be thought of as the first committed step in metazoan fertilization.External links
- Glycolysis Regulation at Cliffsnotes.com