CHAPTER 24: Unit 13. Amino Acids and Proteins Degradation

Enzymes in the stomach and small intestine break down proteins into amino acids. The protein is helping the body to produce amino acids which is helping in building of new proteins.  HCl in the stomach and other hormones help the digestive processes. The pH at the stomach is around 2. HCl denatures the proteins in the stomach and activates enzymes such as pepsin that starts hydrolyzing the peptide bonds. Other enzymes such as trypsin and chymotrypsin ate finishing the hydrolysis of peptides to amino acids which then they are absorbed through the intestine to the blood stream.The figure below shows the small intestine and location of the acinar cells of pencrease where trypsin and other enzymes reside:

Reference: https://courses.lumenlearning.com/suny-ap2/chapter/protein-metabolism/

The video below explains the protein degradation:

Proteins Turnover:

The proteins turnover is caused by synthesis and degradation of the proteins in the human body. Such turn is helping the protein to function at its optimum.There 4 balances in which proteins are turned over:Reference: http://www2.csudh.edu/nsturm/CHE452/12_ProteinNH3%20Met.htmProtein Balance: interrelationship between protein synthesis and degradation (proteolysis).Positive Nitrogen Balance: when dietary intake of proteins is greater than the requirement for endogenous protein synthesis.Neutral Nitrogen Balance: dietary protein intake and endogenous proteins are maintained at a stable level (equilibrium).Negative Nitrogen Balance: if protein intake is insufficient or if the balance of amino acids is incorrect for synthetic needs, endogenous protein is metabolized to liberate free amino acids forThe figure below illustrates these balances in the protein turnover:

Reference: http://www2.csudh.edu/nsturm/CHE452/12_ProteinNH3%20Met.htm

The video below illustrates the turnover of the protein:

Degradation of Amino Acids:

If one eats extra protein, the body will utilized the needed ones, the extra proteins and amino acids are degraded.The α – amino group amino acids are converted into α – keto group amino acids which can enter into different metabolism pathways such citric cycle, synthesis of fatty acids, ketone and glucose.The degradation of amino acids is shown in the two reactions below:

Reference: https://bio.libretexts.org/Bookshelves/Cell_and_Molecular_Biology/Book%3A_Cells_-_Molecules_and_Mechanisms_(Wong)/5%3A_Metabolism_I_%E2%80%93_Catabolic_Reactions/5.9%3A_Amino_Acid_Degradation

Reference: https://bio.libretexts.org/Bookshelves/Cell_and_Molecular_Biology/Book%3A_Cells_-_Molecules_and_Mechanisms_(Wong)/5%3A_Metabolism_I_%E2%80%93_Catabolic_Reactions/5.9%3A_Amino_Acid_Degradation

The videos below illustrate the degradation of amino acids:

Transamination:

The degradation of amino acids occur in the liver. The transamination reaction includes the conversion of an α – amino group from amino acid into α – keto acid. Such reaction yields a new amino acid and a new α – keto acid.The enzyme needed for such reaction is called aminotransferase.

Reference: http://www.dbriers.com/tutorials/2012/12/amination-vs-transamination/

Example of transamination reactions are given below:

Reference: https://saylordotorg.github.io/text_the-basics-of-general-organic-and-biological-chemistry/s23-07-stage-ii-of-protein-catabolism.html

The video below illustrates the transamination process:

Oxidative Deamination:

In the oxidative deamination process, the amino group in glutamate is removed as ammonium group and an α – keto glutamate which can be used in the transamination with amino acid. Such reaction is utilizing the enzyme glutamate dehydrogenate and the coenzyme NAD+. The oxidative deamination reaction is shown below:

References:

The video illustrates the oxidative deamination: