Week 6: Amino Acid Catabolism & Synthesis

List the glucogenic amino acids

Alanine, arginine, aspartate, asparagine, cysteine, glutamate, glutamine, glycine, histidine, methionine, proline, serine, valine

List the ketogenic amino acids

Leucine, lysine

List the amino acids that are both glucogenic and ketogenic

Isoleucine, phenylalanine, threonine, tryptophan, tyrosine

Glutamate and glutamine

Energy source, ammonia transport, urea production

Asparagine and aspartate

Breakdown to oxaloacetate, collecting and eliminating amino nitrogen (Asp)

Alanine

Converted to pyruvate in the liver for either TCA cycle or gluconeogenesis

What is pyruvate the carbon skeleton of?

Alanine

What is oxaloacetate the carbon skeleton of?

Aspartate

What is coupled with the transamination of glutamate to alpha-ketoglutarate?

Conversion of pyruvate to alanine

Tyrosine

Derived from phenylalanine (Phe hydroxylase), converted to DOPA (tyrosinase)

Phenylalanine hydroxylase/biopterin deficiency

Phenylketonuria

Tyrosinase deficiency

Albinism

Tyrosine transaminase deficiency

Tyrosinemia type 2

Homogentisic oxidase deficiency

Alkaptonuria

Fumarylacetoacetate hydrolase deficiency

Tyrosinemia type 1

Tryptophan

Serotonin/melatonin and niacin synthesis

Tryptophan metabolism disorders

Ketoadipic aciduria, glutaric aciduria type 1

Lysine

Carnitine formation or conversion to acetyl-CoA

Methionine metabolism disorders

Homocystinuria, propionic acidemia

Methionine

Conversion to cysteine and succinyl-CoA

What cofactor helps with the reverse reaction from homocysteine to methionine?

Cyanocobalamin (B12)

Cysteine

Synthesis of proteins, taurine, glutathione, degraded to pyruvate and sulfite

What are the BCAAs?

Leucine, isoleucine, and valine

What enzyme degrades the BCAAs?

Branched chain alpha-keto acid dehydrogenase (BCKAD)

What does a BCKAD deficiency lead to?

Maple syrup urine disease

Arginine

Generates alpha-ketoglutarate, converted to creatine

Histidine

Generates alpha-ketoglutarate and carnisine, forms histamine

Proline

Forms glutamate semialdehyde, then glutamate

Threonine metabolism disorders

Propionic acidemia, methylmalonic acidemia

Threonine

Conversion to succinyl-CoA, pyruvate (via glycine and serine), or acetyl-CoA

Serine

Deaminated to pyruvate (serine dehydratase)

Describe the relationship between glycine and serine

Produced reversibly from one another, requires B9

Glycine metabolism disorder

Nonketotic hyperglycinemia

List the essential amino acids

Proline, valine, threonine, tryptophan, isoleucine, methionine, histidine, arginine, leucine, lysine

List the nonessential amino acids

Alanine, asparagine, aspartate, cysteine, glutamate, glutamine, glycine, proline, tyrosine, serine

What is the carbon skeleton for glutamate and glutamine?

Alpha-ketoglutarate

What is the carbon skeleton for aspartate?

Oxaloacetate

What is the carbon skeleton for alanine?

Pyruvate

What is the precursor for serine formation?

D-3-phosphoglycerate

In the final step of serine biosynthesis, what enzyme is deficient and what is the associated pathology?

Phosphoserine phosphatase, Williams syndrome

What are the characteristics of Williams syndrome?

SVAS, mental retardation, facial deformities

How can glycine be synthesized?

Transamination from glutamate, conversion from serine or choline, synthesis from ammonia and carbon dioxide via GSC

Which AA is the precursor for tyrosine synthesis?

Phenylalanine

Which AA is the precursor for cysteine synthesis?

Methionine

How is proline synthesized?

Glutamate-dependent transamination