Protein - Protein Metabolism:

Question 1

Deamination

Answer 1

Deamination:
* For individual amino acids to be used as an energy source or to be stored as fat, they need to undergo ‘deamination’.
* Deamination = removal of the nitrogen-containing amino group from amino acids and occurs primarily in the liver.
* When the nitrogen group is removed from the amino acid, ammonia is formed which is very toxic.
* To then convert the ammonia to a water-soluble compound, it must go through a series of transformation reactions in the liver known as the ‘urea cycle’ to ensure that it can be excreted by the kidneys.
* The less toxic, water-soluble compound formed is ‘urea’, which is filtered out by the kidneys as part of urine.
Deamination = de-(of/removal) + amine (amine group)

Question 2

Glucose / ketones production

Answer 2

• Following deamination (the removal of the amine group), the remaining fragments of amino acids may be used to produce glucose or ketones. These can be used as energy or to become energy storage.

Question 3

Urea Cycle

Answer 3

• Ammonia formed by deamination needs to be converted to ‘urea’ to ensure its safe removal from the body. This involves the Urea Cycle, which takes place in hepatocytes (liver cells).
• The Urea Cycle is the sole endogenous source of the amino acids arginine and citrulline, plus ornithine (an important liver support and detox agent)
• Impairments of the liver’s Urea Cycle can lead to symptoms of ‘hyperammonaemia’. These include:
  o Chronic fatigue, headache, irritability, nausea and diarrhoea, poor concentration, confusion, intolerance of high protein foods.
  Endogenous = made within the body
  Video: www.youtube.com/watch?v=c_-lwMgBsDE&t=650s

Question 4

Hyperammonaemia

Answer 4

• Impairments of the liver’s Urea Cycle can lead to symptoms of ‘hyperammonaemia’. These include:
  o Chronic fatigue, headache, irritability, nausea and diarrhoea, poor concentration, confusion, intolerance of high protein foods.
• Hyperammonaemia is a serious metabolic state often associated with liver cirrhosis.
• Avoiding toxins that negatively impact liver function such as drugs, alcohol, cigarettes and heavy metals is important.
  hyper = elevated, ammon-= ammonia, -aemia= in the blood

Question 5

Transamination

Answer 5

• This is an important step in the synthesis of some non-essential amino acids. If a particular non-essential amino acid is not available, the body can make it from another.
• The amino group of an amino acid is transferred onto an enzyme. The enzyme then transfers the amino group on to a ketoacid, thus forming the new amino acid.
• This reaction is dependent on vitamin B6 as a coenzyme, so a B6 deficiency will impair this process.
  o Vitamin B6 is abundant in wholegrains, green vegetables, sunflower seeds, pistachios, walnuts, bananas, lentils, avocados, meat & fish.

Question 6

Protein Turnover

Answer 6

• Proteins in the body are continually being made and broken down – a process known as ‘protein turnover’. For example, enzymes may be recycled in a matter of minutes.
• When body proteins break down, they free amino acids to join the general circulation; these amino acids + diet-derived amino acids = ‘amino acid pool’.
• Amino acids will be utilised or excreted – they are not stored. Essential amino acids generally have a longer half-life as they are more critical to the body in terms of supply.
• It is therefore important to have a regular supply of protein in the diet –particularly proteins containing the essential amino acids.

Question 7

Protein Turnover and stress (own tissues)

Answer 7

• The body will break down its own tissues to obtain essential amino acids if needed and not in the current ‘pool’.
• Stress causes protein losses in areas such as skeletal muscle, due to the catabolic actions of stress hormones e.g. cortisol.
• Chronic stress also impacts the framework of bones, as protein losses can also occur in the extracellular matrix (i.e. collagen). This explains how chronic stress can increase the risk of osteoporosis.
  Catabolism = breaking down complex substances into simpler ones

Question 8

Proteins for energy

Answer 8

• Recall from the deamination slides that excessive protein from the diet will be transformed into energy or energy storage.
• When glucose and fatty acids are limited due to diet or disease, cells are forced to use amino acids for energy production. Think starvation, prolonged fasting and metabolic disorders/disease.
• Since there is no store of amino acids the only available protein in the body is tissue components.
• When the need arises, the body dismantles tissue proteins and uses them for energy. Over time energy deprivation causes lean tissue wasting.