29.9 Catabolism of Proteins: Deamination
2 min read•may 7, 2024
Protein catabolism breaks down proteins into amino acids, then removes their amino groups. This process, called deamination, is crucial for recycling amino acids and managing nitrogen in the body.
transfers amino groups between amino acids and keto acids, using enzymes and cofactors. The resulting products feed into various metabolic pathways, while excess nitrogen is converted to urea for safe excretion.
Protein Catabolism: Deamination
Process of transamination in catabolism
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- Transfers amino group from amino acid to catalyzed by ()
- () cofactor stabilizes negative charge on α-carbon of amino acid during reaction as electron sink
- Amino group transferred from amino acid to PLP forms () and α-keto acid
- PMP transfers amino group to another α-keto acid regenerates PLP and produces new amino acid ( and )
Conversion of amino acids to keto acids
- α-amino group of amino acid forms with aldehyde group of PLP
- tautomerizes resulting in formation
- Quinonoid intermediate hydrolyzes releasing α-keto acid product and forming PMP
- PMP forms Schiff base with another α-keto acid substrate ( and )
- Schiff base tautomerizes forming second quinonoid intermediate
- Second quinonoid intermediate hydrolyzes releasing new amino acid product and regenerating PLP
Regeneration of pyridoxal phosphate
- PMP formed during first half-reaction contains amino group from original amino acid substrate
- PMP forms Schiff base with new α-keto acid substrate
- Schiff base tautomerizes forming quinonoid intermediate
- Quinonoid intermediate hydrolyzes releasing new amino acid product and regenerating PLP
- Regenerated PLP available to participate in another round of transamination completing catalytic cycle
Protein Breakdown and Nitrogen Metabolism
- initiates protein catabolism by breaking down proteins into individual amino acids
- removes amino groups from amino acids, catalyzed by
- produced during deamination is toxic and must be eliminated
- converts ammonia into urea for excretion, maintaining in the body
Key Terms to Review (22)
Alanine: Alanine is a non-essential amino acid that is commonly found in proteins. It plays a crucial role in various biochemical processes, including protein synthesis, energy production, and amino acid metabolism.
Aminotransferases: Aminotransferases, also known as transaminases, are a class of enzymes that catalyze the transfer of amino groups from one molecule to another. These enzymes play a crucial role in the metabolism of amino acids and the regulation of nitrogen balance within the body.
Ammonia: Ammonia is a colorless, pungent gas with the chemical formula NH3. It is an important compound in organic chemistry, serving as a Lewis base and playing crucial roles in the basicity of amines as well as the catabolism of proteins through deamination.
Glutamate: Glutamate is a nonessential amino acid that plays a crucial role in protein catabolism and the deamination process. It is a key intermediate in the metabolic pathway that breaks down amino acids derived from dietary proteins.
Glutamate Dehydrogenase: Glutamate dehydrogenase is an enzyme that catalyzes the reversible oxidative deamination of glutamate to alpha-ketoglutarate and ammonia. It plays a crucial role in the catabolism of proteins by facilitating the breakdown of amino acids and the entry of their carbon skeletons into central metabolic pathways.
Nitrogen Balance: Nitrogen balance is the relationship between the amount of nitrogen an organism takes in and the amount it excretes. It is a measure of the body's ability to maintain adequate levels of nitrogen-containing compounds, such as proteins, for proper physiological function.
Oxidative Deamination: Oxidative deamination is the process by which amino acids are broken down, where the amino group (-NH2) is removed from the amino acid molecule and replaced with a keto group (-C=O). This process is a crucial step in the catabolism of proteins, as it allows the body to convert the nitrogen-containing components of amino acids into a form that can be excreted.
PLP: PLP, or pyridoxal 5'-phosphate, is a coenzyme derived from vitamin B6 that plays a crucial role in the catabolism of proteins through the process of deamination. It serves as a cofactor for numerous enzymes involved in amino acid metabolism.
PMP: PMP, or Protein Metabolic Pathway, is a crucial process in the catabolism of proteins, specifically the deamination step. It involves the breakdown of amino acids, the building blocks of proteins, to generate energy and other essential metabolites for the body.
Proteolysis: Proteolysis is the breakdown or degradation of proteins into smaller peptides or amino acids. It is a crucial process in the catabolism of proteins, as it allows the body to utilize the building blocks of proteins for various metabolic functions.
Pyridoxal Phosphate: Pyridoxal phosphate is a cofactor derived from vitamin B6 that plays a crucial role in the catabolism of proteins, particularly in the process of deamination. It is an essential component of various enzymatic reactions involved in amino acid metabolism.
Pyridoxamine Phosphate: Pyridoxamine phosphate is a coenzyme form of vitamin B6 that plays a crucial role in the catabolism of proteins through the process of deamination. It serves as a cofactor for enzymes involved in the breakdown of amino acids, facilitating the removal of amino groups from these molecules.
Pyruvate: Pyruvate is a key intermediate molecule in cellular metabolism, serving as a central hub that connects various metabolic pathways. It is the final product of glycolysis, the process of breaking down glucose to generate ATP, and plays a crucial role in energy production, biosynthesis, and other essential metabolic processes within the body.
Quinonoid Intermediate: A quinonoid intermediate is a reactive chemical species that arises as an intermediate in various biochemical reactions, particularly those involving the catabolism of amino acids. This transient structure is characterized by the presence of a quinone-like moiety, which plays a crucial role in the enzymatic transformations that occur during protein degradation.
Schiff base: A Schiff base is a compound featuring a nitrogen atom double-bonded to a carbon atom, which is also bonded to an aryl or alkyl group but not a hydrogen atom, created by the condensation of an amine with an aldehyde or ketone. In the context of glycolysis, it plays a role in the enzymatic conversion of intermediates.
Schiff Base: A Schiff base is a functional group that consists of a carbon-nitrogen double bond, where the nitrogen atom is connected to an aryl or alkyl group rather than hydrogen. Schiff bases are formed through the condensation reaction between a primary amine and an aldehyde or ketone, and they play important roles in various biological processes.
Transaminases: Transaminases, also known as aminotransferases, are enzymes that catalyze the transfer of an amino group from one molecule to another. They play a crucial role in the catabolism of proteins by facilitating the deamination process, which is the removal of the amino group from amino acids.
Transamination: Transamination is a fundamental biochemical reaction in which an amino group is transferred from one organic molecule to another, typically from an amino acid to a keto acid. This process is crucial for the synthesis and catabolism of amino acids, as well as the regulation of nitrogen balance in the body.
Transimination: Transamination is a chemical reaction that transfers an amino group from one amino acid to a keto acid, transforming them into a new amino acid and a new keto acid. This process is essential for the catabolism of proteins, allowing the body to repurpose amino groups for the synthesis of new compounds.
Urea Cycle: The urea cycle, also known as the ornithine cycle, is a metabolic pathway that converts the toxic waste product ammonia into urea, which can be safely excreted from the body. This process is crucial for the catabolism of proteins, as it allows for the disposal of the nitrogen-containing byproducts of amino acid breakdown.
α-Keto Acid: An α-keto acid, also known as an oxo-acid, is a type of organic compound that contains a ketone group (C=O) at the alpha carbon position relative to the carboxyl group (COOH). These compounds are important intermediates in various metabolic pathways, particularly in the catabolism of amino acids and the citric acid cycle.
α-Ketoglutarate: α-Ketoglutarate is a key intermediate in the citric acid cycle, also known as the tricarboxylic acid (TCA) cycle. It is an important metabolic compound that plays a central role in energy production and the catabolism of proteins.