AMAC

Chapter 19: Amino Acids - Disposal of Nitrogen

Introduction

  • Overview of amino acids and their significance in nitrogen disposal within metabolism.

Urea Cycle

Essential Reactions

  • The Urea Cycle is a crucial metabolic pathway for energy metabolism, responsible for the disposal of excess nitrogen from amino acids.

Sources and Fates of Amino Acids

  • Amino acids derive from dietary proteins and play various roles in the body, including energy produing of proteins with ubiquitin for destruction by the proteasome.

Digestion of Dietary Proteinsction, synthesis of proteins, and nitrogen disposal.

Protein Degradation Pathways

Ubiquitin-Proteasome System

  • Major pathway for protein degradation involving tagg

Role of Proteolytic Enzymes

  • Breakdown of dietary proteins occurs in the gastrointestinal tract by proteolytic enzymes, which hydrolyze peptide bonds to form smaller peptides and amino acids.

Pancreatic Proteases

  • Major Pancreatic Proteases

    • Five key proteases involved:

      • First three: Serine endopeptidases

      • Last two: Exopeptidases

  • Each protease has specific peptide bonds susceptible to hydrolysis.

Genetic Disorders

Cystinuria vs. Cystinosis

  • Cystinuria involves a genetic defect leading to improper cystine transport, causing formation of cystine crystals and tissue damage, distinct from cystinosis.

Aminotransferase Reactions

Key Reactions

  • α-Ketoglutarate as Amino-Group Acceptor

    • Transamination reactions where amino acids transfer their amino groups to α-ketoglutarate.

  • Enzymatic Reactions:

    • Alanine aminotransferase (ALT)

    • Aspartate aminotransferase (AST)

Pyridoxal Phosphate Interconversion

Aspartate Aminotransferase Reaction

  • Cyclic interconversion of pyridoxal phosphate and pyridoxamine phosphate crucial for transamination processes.

Toxic Mushroom Poisoning

Serum Enzyme Patterns

  • Examination of serum ALT and bilirubin post-exposure to the toxic mushroom Amanita phalloides, highlighting liver damage.

Oxidative Deamination

Glutamate Dehydrogenase

  • Enzyme responsible for oxidative deamination, converting glutamate to α-ketoglutarate while producing ammonia.

Combined Enzyme Actions

Aminotransferase and Glutamate Dehydrogenase

  • Overview of how these two enzymes collaborate in amino acid catabolism and nitrogen elimination.

Ammonia Transport

To the Liver

  • Mechanism for transporting ammonia from peripheral tissues to the liver for urea synthesis.

Urea Cycle Reactions

Summary

  • Detailed outline of the reactions involved in the urea cycle for nitrogen disposal.

Flow of Nitrogen to Urea

Mechanism

  • Nitrogen from amino acids is collected as ammonia and aspartate for urea synthesis.

N-Acetylglutamate Formation

Role as Allosteric Activator

  • Key regulatory role in urea cycle, specifically activating carbamoyl phosphate synthetase I.

Ammonia Hydrolysis

Glutamine Hydrolysis

  • Conversion of glutamine to ammonia, involving hydrolytic reactions.

Glutamine Metabolism

Synthesis and Role

  • Overview of glutamine synthesis and its importance in nitrogen metabolism.

Ammonia Metabolism

Urea Measurement

  • Urinary Urea Nitrogen (UUN) and Blood Urea Nitrogen (BUN) measurement significant for assessing nitrogen disposal efficiency.

  • Enzymes involved: Glutamate dehydrogenase, glutamine synthetase, and carbamoyl phosphate synthase I.

Treatment for Urea Cycle Defects

Phenylbutyrate Administration

  • Management strategy for patients with urea cycle disorders to enhance ammonia excretion.