2nd Year DENT Lecture 1 Objectives on Amino Acid Catabolism and Transaminases

Amino Acid Catabolism

• The first step in amino acid catabolism is deamination, which involves the removal of an amino group from an amino acid.
• Free ammonia is typically converted to urea by humans for disposal.

Deamination Methods

• There are two main methods of amino acid deamination: oxidative deamination and transdeamination.
• Oxidative deamination produces ammonia, NADH, and α-ketoglutarate as products, as seen in the deamination of L-glutamate.

Nitrogen Disposal

• Nitrogen disposal from amino acids is achieved through the urea cycle, where ammonia is converted to urea.

Urea Cycle

• The form of nitrogen excreted by humans in urine is urea.
• The urea cycle is a degradative pathway for all amino acids except lysine, threonine, and proline.

Transaminases Enzymes

• Transaminases enzymes play a crucial role in amino acid metabolism.
• ALT (alanine transaminase) and AST (aspartate transaminase) enzymes are mainly located in the liver and kidneys.
• The biosynthesis of transaminases enzymes is induced by hormones such as glucocorticoids and thyroxine.

Clinical Significance

• Increased plasma levels of ALT and AST are clinically significant, indicating liver damage or disease.

Transdeamination

• The enzyme responsible for transdeamination is glutamate dehydrogenase, which combines transamination and deamination processes.
• The fate of the ammonia removed during transamination is its conversion to urea in the urea cycle.

Glucogenic Amino Acids

• After oxidation, glucogenic amino acids are converted to glucose or ketone bodies.
• The primary source of amino acids for non-essential amino acid synthesis is other amino acids.

Urea Excretion

• Essential amino acids are mainly excreted in urine as urea.
• The major fate of amino acids from protein breakdown is their oxidation to produce energy.