04: Amino Acid Metabolism and Urea Cycle

Catabolism of amino acids involves the removal of nitrogen which is released as: ________

ammonia, urea, and uric acid

Protein Digestion: In the stomach

HCl denatures the protein

HCl activates _______,which breaks complex proteins to polypeptides

pepsinogen to form pepsin

Protein Digestion: In the pancreas

The protease enzymes _________ break downpolypeptides to oligopeptides

trypsin,chymotrypsin, elastase,and carboxypeptidase

Protein Digestion: In the small intestine

_________ cleave oligopeptidesto small peptides and free amino acidswhich are taken into the liver

Aminopeptidases

Catabolism of amino acids: Transamination

• Reaction(s) involving the removal of nitrogen from amino acids

• Removal of α-amino group

• Reaction involves the transfer of the α-amino group to α-ketoglutarate to form ______

• Reaction is catalyzed by an enzyme (_________) along with a prosthetic group (__________)

forms glutamate (Glu,E) and a-ketoacid, enzymes aminotransferase, pyridoxal phosphate

Transamination (Catabolism of amino acids) Two aminotransferases are:

Alanine aminotransferase (ALT), Aspartate aminotransferase (AST)

______ (prosthetic group) transfers the amino group

Pyridoxal phosphate

_________are all α-keto acids

• They have a –C=O group on the carbon adjacent to the –COOH group

Pyruvate, oxaloacetate, α-ketoglutarate

Catabolism of Amino Acids

• Oxidative deamination results in removal of the amino group as free ammonia

• Enzyme: ________

• Uses NAD+ or NADP+

• occurs in the liver and kidney

• Products are______

glutamate dehydrogenase, a-ketoacids and ammonia (NH3)

Ammonia (product of catabolism of amino acid) is toxic, and is converted to ____ in the liver

urea

Urea is the major disposal form of amino groups from amino acids

• Derived from ________

• 90% of the nitrogenous components of urine

ammonia, aspartate (Asp,D) and carbon dioxide

*Urea is produced in the _______, transported in the blood to the ______, and excreted in urine

urea is produced in liver and transported to kidneys

Some urea is cleaved by bacterial ______ in the intestine into ammonia which is removed in the feces

urease

In ______, high levels of urea are found in the blood

kidney failure

Nitrogen elimination

• Removal of α-amino group of AA: _____ and _____

• NH3 is toxic

  • Converted to urea in the liver

  • Eliminated in the urine

Transamination, Oxidative deamination

______ amino acids

• Their catabolism yields pyruvate or intermediates of the TCA cycle

• These are substrates for gluconeogenesis

Glucogenic

_____ amino acids

• Their catabolism yields acetoacetate or its precursors, acetyl CoA and/or acetoacetyl CoA

• These are substrates for ketogenesis

• They do not give rise to the net formation of glucose

Ketogenic

List the Essential Glucogenic Amino Acids

Histidine (His,H), Methionine (Met,M), Threonine (Thr,T), Valine (Val,V)

List the Essential Glucogenic AND ketogenic amino acids

Isoleucine (Ile, I), Phenylalanine (Phe,F), Tryptophan (Trp,W)

List the Essential ketogenic amino acids

Leucine (Leu,L), Lysine (Lys,K)

List the Family of Amino Acids

Glutamate (Glu,E), Aspartate (Asp,D), Serine (Serine,S), Alanine (Ala,A), Aromatic Amino Acids (Phe,F; Tyr,Y; Trp,W), Histidine (His,H)

Source: Glutamate

a-ketoglutarate

Source: Aspartate

Oxaloacetate (OAA)

Source: Serine

3-phosphoglycerate

Source: Alanine

Pyruvate

Source: Aromatic Amino Acids

Phosphoenolpyruvate, erythrose 4-phosphate

Source: Histidine

ribose 5-phosphate