Tissue-specific peptide pools. Generation and function

Systematic analysis of several tissue extracts for peptide components follo wed by bioactivity studies leads to formulation of the concept of "tissue-s pecific peptide pools" According to that concept the endogenous proteolysis of proteins with well-established functions, such as hemoglobin, actin, an d cellular enzymes in tissues leads to formation of the sets (or pools) of bioactive peptides. The sets are tissue-specific on one hand and conservati ve in a given tissue at normal conditions on the other. The content and the composition of pool components are sensitive both to pathologies linked wi th alterations of tissue metabolism and to prolonged physiological changes. In vivo formation of fragments of functional proteins includes several con secutive proteolytic stages inside the cells and further release of bioacti ve compounds into the surrounding medium. The effects of pool components ta ke place predominantly at tissue and cellular levels, their effects being r elated to stimulation or inhibition of cell growth, induction of cell diffe rentiation, and death. The above-mentioned features lead to the proposal th at the main in vivo function of components of tissue-specific peptides is m aintenance of tissue homeostasis, i.e., the normal ratio of functional, div iding, differentiating, and dying cells of tissues. Components of tissue-sp ecific peptide pools display several features distinguishing them from "cla ssical" peptide hormones and neuromediators. Summarizing, a novel peptiderg ic regulatory system is considered.