Allosteric Enzyme Regulation and Covalent Enzyme modification
Both reversible and irreversible covalent modification of enzymes play important roles in regulation of enzyme function.
Enzyme Regulation – Allosteric Enzyme Regulation and Covalent modification is topic of our this post. You would learn what is enzyme regulation and Allosteric Enzyme Regulation and Covalent modification.
A regulatory enzyme is an enzyme in a biochemical pathway which through its responses to certain signals, regulates the pathway’s activity.
For example- In cellular metabolism, groups of enzymes work together in sequential pathways to carry out a given metabolic process. The activities of metabolic pathways in cells are regulated by control of the activities of regulatory enzymes.
Regulation of Enzyme Activity:
- Allosteric regulation
- Covalent modification
- Proteolytic cleavage of proenzyme
We only discuss about the Allosteric regulation and Covalent modification in this Post.
Allosteric regulationis the regulation of activities of an enzyme or a protein caused by the binding of modulators ( or effectors) at the site other than the active site of the enzyme or protein. There are two effects of Allosteric regulationis and two effectors are may be available for the effects-
Effectors may be-
- feed-forward activators or
- feedback inhibitors
when a positive modulator is attached to the Enzyme then the enzyme become more active and when the Enzyme attached with the negative modulator then the enzyme become less reactive.
Covalent Enzyme Regulation:
Reversible covalent modification : The modulation of enzyme activity by the attachment or release of small groups plays a very important role in metabolic control. Probably the most universal, and certainly the most well understood, is the phosphorylation of specific serine, threonine or tyrosine groups.
Irreversible covalent modification : Proteolytic cleavage of specific peptide bonds is often used to activate enzymes. Since proteolysis is essentially irreversible, turning the activity off requires another mechanism, often binding of inhibitory proteins.
Reversible Covalent Modifications:
- Reversible covalent modifications require expenditure of energy and are often used in signaling from extracellular messages.
- In contrast, noncovalent interactions are reversible with no metabolic energy expended and sense conditions within a cell.
- Reversible covalent modifications that are known to alter enzyme activity include:
i. Phosphorylation of serine, threonine or tyrosine and less frequently aspartate and histidine residues.
ii. Acetylation of lysine or amino terminal groups.
iii. Methylation of glutamate or aspartate residues
iv. Nucleotidylation of tyrosine residues
v. ADP ribosylation primarily of arginine residues.
For example we discuss the Phosphorylation and Dephosphorylation –
Phosphorylation and Dephosphorylation
- Phosphorylation reactions are catalyzed by a family of enzymes called protein kinases that use adenosine triphosphate (ATP) as a phosphate donor.
- Phosphate groups are cleaved from phosphorylated enzymes by the action of phosphoprotein phosphatases
- Amino acids with –OH groups are targets for phosphorylation.