Metabolism of Nitrogenous Compounds

Metabolism of Nitrogenous Compounds

• This presentation covers the metabolism of various nitrogen-containing compounds, particularly amino acids.

Learning Objectives

• Describe protein digestion.
• Explain reactions separating amino groups from amino acids.
• Detail the fate of carbon skeletons.
• Describe glucogenic and ketogenic amino acids.
• Introduce biogenic amines.
• Provide examples of nitrogenous compounds.

Contents

• Amino Acids (Proteins)
• Biogenic Amines
• Porphyrins
• Nucleobases

Overall Picture of Amino Acid Metabolism

• Dietary protein is degraded into amino acids.
• Amino acids can be used for energy production or to synthesize body protein.
• Transamination transfers amino groups to a-ketoglutarate, creating glutamate.
• Keto acids can be converted to glucose or fat.
• Ammonia is converted to urea.
• Nonessential amino acids (AAs) can be synthesized by the body.

Protein Digestion

• Proteins are too large to be directly absorbed.
• Hydrolysis is necessary to break proteins into smaller peptides and amino acids.
• Enzymatic reactions in the stomach and small intestine digest proteins.
• Proteolytic enzymes (e.g., pepsin, trypsin) break peptide bonds.
• Hydrolysis breaks proteins into di- and tripeptides absorbed by small intestine

Amino Acid Metabolism

• Proteins are not stored for future energy use.
• Protein is either degraded or used for synthesis.
• Nitrogen removal produces ammonia (toxic).
• Degradation of an amino acid produces urea (less toxic) to be excreted.

Amino Acid Degradation

• Separation of amino group by transamination and oxidative deamination.
• Metabolism of carbon skeleton: amino acid carbon skeletons transformed into intermediates for other metabolic pathways (Krebs cycle/citric acid cycle)
• Formation of Glutamate (intermediary in amino acid metabolism).

Oxidative Deamination

• Removal of amino group by oxidative deamination is a reversible process.
• Converts amino acids to alpha-ketoacids.
• Releasing Ammonia that will eventually be converted to Urea.

Urea Cycle

• Converts ammonia into urea, a less toxic compound.
• Involves several reactions in the liver.
• Aspartate and ammonia are used to produce urea.
• Urea is excreted in urine

Porphyrin Degradation

• Disorders in porphyrin degradation can cause jaundice.
• Some toxic intermediate products can be formed due to the inability to degrade porphyrins correctly or be excreted.

Nucleotide Metabolism

• Nucleotides are composed of three parts: a phosphate group, a pentose sugar, and a nitrogenous base.
• Nucleotides are broken down and synthesized from simpler precursor molecules.
• Nucleotide synthesis requires nitrogen and carbon.
• Purines and pyrimidines are two types of nitrogenous bases of nucleotides.
• Nucleotide degradation produces simpler molecules and nitrogenous bases

Biogenic Amines

• Molecules derived from amino acids with neurotransmitter functions.
• Many are involved signaling and regulation in the body.
• Often synthesized in tissues and organs.
• Several neurotransmitters are biogenic amines.