Amino Acid Metabolism Flashcards
Forms of ammonia transport
Glutamine
Alanine
Normal blood urea concentration
15-40mg/dl
Sources of glycine
Serine
Threonine by threonine alsolase
NH4+ + CO2 by glycine synthase
Glyoxylate/glutamate/alanine by glycine aminotransferase
Components of glutathione
Glycine+ Cysteine + glutamate
Components of creatine
Glycine + Methionine + Arginine
BC ā ketoacid dehydrogenase complex
Decarboxylase + transacylase + dihydrolipoyl dehydrogenase
Sources of serine
- Phosphoglycerate
- Glycine
- Transamination of hydroxypyruvate with alanine
Functions of serine
- Forms glycine
- Forms Cysteine and alanine
- Azaserine- anticancer
Cycloserine- anti TB - Serine proteases (active sites of enzymes with Ser)
- Selenocysteine
Selenocysteine found in
Active sites of
- Thioredoxin reductase
- Glutathione peroxidase
- Deiodinase
- Selenoprotein P
Threonine degraded to
- Ā keto butyric acid by threonine dehydratase
2. Gly + acetaldehyde by threonine aldolase
Methionine functions
Cysteine synthesis
SAM which is methyl donor
Cysteine degraded to
B mercaptopyruvate
B mercaptoethanolamine
Functions of Cysteine
- Glutathione formation
- Sulfur metabolism
- Forms PAPS as sulfur donor and helps in conjugation
Normal homocysteine blood levels
5-15 micromol/L
Glutamic acid functions
- Ākga formation
- Formation of NAG
- Synthesis of glutamine
- Helps in NO synthesis
- GABA synthesis
- Glutathione synthesis
Functions of glutamine
- Forms glutamate in rxn that is important in trapping and transporting ammonia
- N 3, 9 of purines
- N3 of pyrimidines
- Source of NH2 of guanine and cytosine
- Conjugating agent
Functions of aspartic acid
- Transamination to form OA and GLUTAMATE
- Malate aspartate shuttle
- Urea cycle
- Purine pyrimidine synthesis
Aspargine
L asparagine anticancer drug against leukemias and lymphomas
Functions of lysine
- Collagen
- Precursor of carnitine
- Can form Schiff bases
- Bacterial decarboxylation forms cadaverine
Histamine
- Smooth muscle contraction
- Inc. vascular permeability
- Inc. acid secretion
- Low BP
- produced by platelets, basophils, mast cells
- cause anaphylaxis
Precursor of NO
Arginine
Functions of NO
- Vasodilator
- Inhibits platelet aggregation
- NT associated with memory
- Involved in bactericidal action of macrophages
- Smooth muscle relaxation
- Can treat angina and hypertension
Functions of phenylalanine and tyrosine
- Synthesis of catecholamines in renal medulla and sympathetic ganglia
- Thyroid hormones syn.
- Synthesis of melanin
Serotonin functions
- Vasoconstrictor
- Excitatory NT
- Causes peristalsis
- Influences behavior patterns
- Regulates prolactin secretion
- Sleep inducer
- Regulates BP and body temp.
Transamination
- exchange of amino grp bw alpha AA and alpha keto acid forming new AA
- mostly, amino grp is accepted by alpha KGA to form glutamic acid
- catalysed by amino transferases
- require pyridoxyl phosphate
- reversible so Synth. and degrad.
- provides non essential AA during protein synthesis
- ## transaminases used as diagnostic markers
Energetics of urea cycle
4 ATP used
Fumarate to malate to OAA generates 1 NADH = 2.5 ATP
NET = 1.5 ATP used
Regulation of urea cycle
- Activity inc. on starvation
Regulatory enzyme - CPS1
+ NAG
One carbon groups
Formyl Formimino Methenyl Hydroxymethyl Methylene Methyl - they are carried by THFA
Contributing AA for one carbon groups
- Serine to glycine
- Glycine cleavage system
- Histidine through FIGLU
- Tryptophan
- Choline
Used of 1C groups
- C2, C8 of purine
- Formulation of methionyl tRNA
- Glycine
- Serine
- Choline
- Deoxy TMP
- Transmethylation rxns
- Excreted as CO2
Glycine cleavage system
- Oxidative deamination of gly
- gives NH3, CO2, methylene THFA
System contains
1. Glycine decarboxylase with PLP
2. Amino methyl transferase
3. Methylene THFA synthase
4. NAD+ dep. lipoamide dehydrogenase
Glucogenic pathway of glycine metabolism
Glycine to serine
Serine to pyruvate by serine dehydratase
Functions of glycine
- C4,5,7 of purine ring
- Heme synthesis (aminolevulinic acid formation)
- Creatine, creatine phosphate, creatinine syn.
- Glutathione formation
- Conjugating agent in bile
- Inhibitory neurotransmitter
Intermediates in creatine formation
KIDNEY Glycine + arginine Guanidoacetate LIVER \+ SAM = creatine MUSCLE -H2O = creatinine -ATP = creatine phosphate - Lohmanns rxn
Normal serum creatinine and creatine levels
Creatinine - 0.7-1.4mg/dl
Creatine - 0.2-0.4mg/dl
Catabolism of serine products
- Deamination to pyruvate
- Transamination to hydroxypyruvate
- Glucogenic
Sources of alanine
- Transamination of Pyruvate with glutamate
2. Glucose alanine cycle
Carnosine
- beta alanine + histidine
- major constituent of muscles
- can activate myosin contraction
