Lysine: Sources, Metabolism, Physiological Importance, and Use as a Supplement.

This article provides a comprehensive review and explores the gaps in current knowledge of lysine metabolism in humans and its potential nutritional and therapeutic indications. The first part of this study examines lysine sources, requirements, transport through the plasma membrane, lysine catabolism, and its disorders. The central part is focused on post-translational modifications of lysine in proteins, primarily desmosine formation in elastin, hydroxylation in collagen, covalent bonds with glutamine, methylation, ubiquitination, sumoylation, neddylation, acylation, lactylation, carbamylation, and glycation. Special sections are devoted to using lysine as a substrate for homoarginine and carnitine synthesis and in nutrition and medicine. It is concluded that the identification and detailed knowledge of writers, readers, and erasers of specific post-translational modifications of lysine residues in proteins is needed for a better understanding of the role of lysine in epigenetic regulation. Further research is required to explore the influence of lysine availability on homoarginine formation and how the phenomenon of lysine-arginine antagonism can be used to influence immune and cardiovascular functions and cancer development. Of unique importance is the investigation of the use of lysine in osteoporosis therapy and in reducing the resorption of harmful substances in the kidneys, as well as the therapeutic potential of polylysine and lysine analogs.