Biological Chemistry - Berezov T. T., Korovkin B. F. 1998

Metabolism of Simple Proteins
Reserve Proteins

The term "reserve Proteins" does not refer to specialized protein deposits, but rather to tissue proteins that can be readily mobilized when needed. Following Hydrolysis by specific proteinases, these proteins supply the Amino Acids required for the synthesis of Enzymes, Hormones, and other vital substances. Animal experiments have demonstrated that starvation leads to a disproportionate loss of mass among different Organs and Tissues, with the Liver showing a significantly greater reduction in mass. Numerous clinical observations in patients likewise indicate that during fasting and severe infectious diseases—conditions marked by accelerated organ breakdown—the mass of The Liver and Muscles decreases first, while the mass of the Brain and Heart remains essentially unchanged. By breaking down liver and Muscle Proteins, the body sustains the normal function of vital organs. Based on these findings, Blood Plasma, liver, and muscle proteins are generally considered to act as "reserves," although these reserves are fundamentally different in nature from carbohydrate reserves (Glycogen deposition in the liver and muscles) and lipid reserves (triacylglycerol storage in adipose depots).

It should nevertheless be emphasized that the body's mechanism for the rapid mobilization of protein resources under extreme conditions (such as starvation, severe intoxication, or blood loss) undoubtedly plays a crucial physiological role.