Lecture 7: Biosynthesis of Amino Acids

name the nonessential amino acids

Alanine, aspartate, asparagine, glutamate, serine

How can you produce alanine?

Synthesized from pyruvate by transformation from glucose (Alanine + a-KG → Pyruvate + Glutamate) performed by ALT enzyme

How can you produce asparagine?

Synthesized by amidation of aspartate, catalyzed by the enzyme asparagine synthetase utilizes ammonia tunnel, requires ATP

(OAA → Aspartate → Asparagine)

How can you produce aspartate?

synthesized from OAA by transamination from glutamate, or can convert asparagine to aspartate by hydrolysis (Deamination)

(Asparagine → Aspartate)

How can you produce glutamate?

transamination via transaminase

(a-KG + AA → Glutamate + a-KA)

reductive amination via glutamate dehydrogenase (GDH)

(a-KG + NH3 + NADPH → Glutamate + NADP+)

hydrolysis via Glutaminase

(Glutamine + H2O → Glutamate + NH3)

Name the conditionally essential amino acids

Arginine, cysteine, glutamine, glycine, proline, tyrosine (R U C Quick Green Pepper)

Synthesizing arginine

synthesized in urea cycle, argininosuccinate is cleaved into fumarate and arginine

Synthesis of creatine

Synthesized from arginine phosphorylated by creatine kinase and plays important roll to maintain constant energy supply in exercising muscles

Synthesis of creatinine

waste product and indicator of renal function, cyclizes and cannot be created into creatine and is thus filtered from the blood

Synthesis of tyrosine

Phenylalanine hydroxylase catalyzes hydroxylation at C4 of the phenol group of phenylalanine to form tyrosine, this enzyme is tetrahydrobiopterin dependent (BH4) which is also a cofactor that is essential for biosynthesis of dopamine, noradrenaline, and serotonin

S - Adenosyl methionine (SAM)

The main methylating agent for 300 metabolites, involved in the synthesis of homocysteine, is the primary active methyl donor

the methionine cycle

Recycling cycle common precursor for SAM a source of sulfur for cysteine synthesis

Glutathione (GSH)

Cellular reducing agent, derived from glu, cys, and gly, can be oxidized and form a dimer (GSSH) or can be reduced

Amino acids as neurotransmitters

Glutamate = main excitatory

aspartate = excitatory

d-serine = Co-agonist of glutamate receptors

glycine = inhibitory

Neurotransmitters from amino acids

• catecholamines: the fight or flight hormone, tyrosine derived, includes dopamine norepinephrine and epinephrine

• GABA: when B6 dependent, inhibitor, glucose → glutamine → Gaba

• Serotonin: Tryptophan