| Function | Example |
|---|---|
| Substrates for protein synthesis | Those amino acids for which there is a codon |
| Regulators of protein turnover | Leucine, arginine? |
| Regulators of enzyme activity | Arginine and N-acetylglutamate synthetase Phenylalanine and phenylalanine hydroxylase activation |
| Precursor of signal transducer | Arginine and nitric oxide |
| Methylation reactions | Methionine |
| Neurotransmitter | Tryptophan, glutamate |
| Ion fluxes | Taurine, glutamate |
| Physiologic molecular precursors | Arginine, glutamine, purines |
| Nitrogen transporters | Alanine, glutamine |
| Circulating transporters | Ceruloplasmin; apolipoproteins Vitamin and hormone binding proteins |
| Messengers/Signals | Insulin, growth factors |
| Movement | Actin, kinesin |
| Immunity | Antibodies, interleukins |
| Growth, differentiation, gene expression | Growth factors, transcription factors |
SOURCE: Adapted from Young and Yu, 1996.
From: 5, The Energy Costs of Protein Metabolism: Lean and Mean on Uncle Sam's Team
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