Protein Metabolism

Describe the physiology and biochemistry of fat, carbohydrate and protein metabolism

Essential amino acids cannot be produced by transamination - they must be supplied in the diet.

Metabolism

Protein catabolism involves the deamination of amino acids. Deamination can occur in one of two ways:

• Oxidative deamination
  Hepatic deamination, removing the amino group to create a ketoacid and ammonia. Ammonia produced in the liver enters the urea cycle and becomes urea, which requires 3 ATP.
• Transamination
  Amino group is transferred by aminotransferases to another amino acid or a ketoacid to produce:
  • Keto acids, which:
    • Enter the citric acid cycle and produce ATP
    • Get converted to glucose or fatty acids
  • Amino groups
    • Enter the urea cycle and become urea

Footnotes

Ammonia can also be produced in the kidney by the deamination of glutamate in the kidney. In this instance:

• It is eliminated directly in urine as ammonium
• Does not enter the urea cycle

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References

1. Chambers D, Huang C, Matthews G. Basic Physiology for Anaesthetists. Cambridge University Press. 2015.