Comprehensive Review of L-Lysine: Chemistry, Occurrence, and Physiological Roles.

L-lysine, an essential amino acid, is indispensable for numerous biological functions, including protein synthesis, collagen crosslinking, mineral absorption, and carnitine biosynthesis. Its biosynthesis occurs via the Diaminopimelate (DAP) pathway in bacteria and plants and the α-aminoadipate (AAA) pathway in fungi and some archaea. Lysine catabolism primarily involves the saccharopine pathway. Lysine deficiencies can lead to connective tissue disorders, impaired fatty acid metabolism, anemia, and protein-energy malnutrition. Commercial production relies predominantly on microbial fermentation using Corynebacterium glutamicum, with strains enhanced through classical and metabolic engineering approaches. With global production exceeding 1 million tons annually, which is largely dominated by Chinese manufacturers, lysine supplements are readily accessible and exhibit absorption rates comparable to those of dietary protein sources. Beyond its nutritional role, lysine is integral to epigenetic regulation via histone modifications and is implicated in diseases, such as hyperlysinemia and pyridoxine-dependent epilepsies, underscoring its vital role in health maintenance and industrial relevance.