Amino Acid and Amine Metabolism

Flashcards reviewing key concepts in amino acid and amine metabolism, including protein digestion, transamination, the urea cycle, carbon skeleton scavenging, detoxification, and renal function.

What are zymogens?

Inactive forms of enzymes that protect organisms from their own digestive enzymes; may require modification for activation.

Where does protein digestion begin?

In the stomach with the enzyme pepsin.

What is the function of pancreatic enzymes?

Proteases that cleave peptide (amide) linkages between amino acids.

What are peptidases?

Enzymes that cleave peptides into smaller individual amino acids or small peptides (di- or tripeptides).

What are some biological roles of amino acids?

Neurotransmitters (or precursors), metabolic intermediates, allosteric regulators, and in the metabolism of other amino acids.

What is transamination?

The process in which an amine group is transferred from an amino acid to an α-keto acid, producing a new amino acid and a new α-keto acid.

What is oxidative deamination?

The process in which an amine group is removed from ammonia, also involving an α-keto acid and generating NADH/H+.

What is the glucose-alanine shuttle?

A metabolic process through which nitrogenous wastes generated in muscle are transferred to pyruvate, generating alanine, which is then transported to the liver for deamination.

What is the role of glutamine synthetase?

It is an ATP-dependent enzyme responsible for the synthesis of glutamine from glutamate and ammonium ion in the liver.

What is the main function of glutaminase?

It deaminates glutamine, yielding glutamate and free ammonia.

What is the urea cycle?

The metabolic pathway that generates urea from carbamoyl phosphate to detoxify and dispose of ammonia.

What is carbamoyl phosphate?

A compound created from ammonia to reduce ammonia levels in the blood and lower the risk for toxicity.

What is the function of carbamoyl phosphate synthetase?

It is an enzyme used to produce carbamoyl phosphate and has two isoforms: CPS-I (mitochondrial) for the urea cycle and CPS-II (cytosolic) for pyrimidine biosynthesis.

What is the difference between ammonotelic and uricotelic organisms?

Ammonotelic organisms eliminate wastes as ammonia, while uricotelic organisms synthesize uric acid and eliminate it in their waste.

What are glucogenic amino acids?

Amino acids that are broken down into products that undergo gluconeogenesis.

What are ketogenic amino acids?

Amino acids that metabolize products into ketone bodies.

What are xenobiotics?

Molecules the body recognizes as foreign and that need to be eliminated.

What is xenobiotic metabolism?

The process by which the body detoxifies and eliminates foreign molecules, creating more water-soluble molecules in two phases.

What occurs during Phase I of xenobiotic metabolism?

Oxidation or cleavage occurs, and xenobiotics become more hydrophilic.

What occurs during Phase II of xenobiotic metabolism?

Conjugation with larger molecules occurs, such as glutathione or glucuronic acid.

What are cytochrome P450 enzymes?

Enzymes that employ NADPH and molecular oxygen to oxidatively modify substrate molecules.

What is the function of monoamine oxidases?

Enzymes that deactivate neurotransmitters by catalyzing the conversion of a primary amine to an aldehyde.

What is the role of glucuronic acid in phase II metabolism?

Conjugation to molecules during phase II metabolism. It is an oxidized form of glucose in which C-6 is oxidized to a carboxylic acid

What is the role of Glutathione (GSH) in phase II metabolism?

Conjugated to xenobiotic via glutathione-S- transferase. It is a tripeptide of glycine, cysteine, and glutamate

What is the glomerulus?

A network of highly porous capillaries in the kidney that act as filters.

What is the role of antidiuretic hormone (ADH)?

It is a peptide hormone that acts via a seven-transmembrane helix-spanning receptor to elevate cytosolic levels of cAMP and facilitate water transport in the kidney.