Protein and AA metabolism Flashcards
Positive nitrogen balance (3 things)
- Intake > output
- Increase in total body protein
- Normal in growth, pregnancy or adult recovery from malnutrition
Negative nitrogen balance (3 things)
- Intake < output
- Net loss of body protein
- Trauma, infection or malnutrition
Cushing’s syndrome (3 things)
- Excessive breakdown of protein
- Due to excess cortisol
- Leads to striae formation (stretch marks)
What controls mobilisation of protein reserves?
Hormones
Where do C atoms for non-essential AA synthesis come from (3 things)?
- Intermediates of glycolysis
- Pentose phosphate pathway
- Krebs cycle
What is glycine used to synthesise (4 things)?
- Purines
- Glutathione
- Haem
- Creatine
What is tryptophan used to synthesise (3 things)?
- Nicotinamide
- Serotonin
- Melatonin
What is cysteine used to synthesise (2 things)?
- H2S
- Glutathione
What is tyrosine used to synthesise (3 things)?
- Catecholamines
- Melanin
- Thyroid hormones
What does histidine synthesise?
Histamine
What does arginine synthesise?
Nitric oxide
What does glutamate synthesise?
GABA
What does serine synthesise?
Sphingosine
Transamination key points (4 things)
- Transfers an amine group from an amino acid to a keto group
- Most aminotransferases use alpha-ketoglutarate to funnel amino group to glutamate
- Need coenzyme pyridoxal phosphate
- Derivative of vitamin B6
Key aminotransferases (4 things)
- ALT (alanine to pyruvate)
- AST (aspartate to oxaloacetate)
- alpha-ketoglutarate to glutamate too
- Measured routinely as part of liver function test
What conditions cause extensive cellular necrosis (3 things)?
- Viral hepatitis
- Autoimmune liver diseases
- Toxic injury
Enzymes used in deamination (3 things)
- Amino acid oxidases
- Glutaminase
- Glutamate dehydrogenase
Urea cycle key points (4 things)
- Occurs in liver and involves 5 enzymes
- Amount of enzymes normally related to need to dispose of ammonia
- Cycle is inducible but not regulated
- Affected by amount of protein in diet
Defects in urea cycle (4 things)
- Autosomal recessive genetic disorders due to enzyme deficiency
- Mutations cause partial loss of enzyme function
- Hyperammonaemia
- Accumulation/excretion of urea cycle intermediates
Symptoms of defects in urea cycle (6 things)
- Vomiting
- Lethargy
- Irritability
- Mental retardation
- Seizures
- Coma
What does the severity of NH3 toxicity depend on (2 things)?
- Nature of defect
- Amount of protein eaten
How to manage urea cycle defects (2 things)
- Low protein diet
- Replace AA in diet with keto acids
What should blood level of NH3 be?
25-40 micromol/L
Potential toxic effects of NH3 (6 things)
- Interference with AA transport & protein synthesis
- Disruption of cerebral blood flow
- pH effects (alkaline)
- Interferance with metabolism of excitatory AA neurotransmitters
- Alteration of blood-brain barrier
- Interference with TCA cycle
