Protein metabolism is a dynamic process, which includes both synthesis and degradation of proteins. Consequently, it is no less important to study and understand the protein catabolism functions, than to determine the role of their synthesis. The review, which is the last part of the discussion concerning the bioregulatory role of proteins and peptides full proteolysis, focuses on the mechanism of protein selection in cytoplasm  and their proteolysis, which has been discovered recently. Proteolysis of these compounds to separate amino acids is one of the fundamental processes, supporting stationary concentration of proteins and peptides in all human body cells.