Protein metabolism sub-model. Overview of the protein metabolism model with arrows describing material flow. AAs are used for protein synthesis in a specific composition satisfying the profile of the tissue protein. Remaining AAs are broken down into TCA metabolites and enter the intermediate metabolism. Protein synthesis and degradation are energy and temperature dependent. The fraction f
of AAs emerging from protein degradation is reused for protein synthesis, and the fraction f
= 1 - f
is broken down.