"N6-{[(2R,3R)-3-methyl-3,4-dihydro-2H-pyrrol-2-yl]carbonyl}-(L)-lysine"@en . "Pyrrolysine (abbreviated as Pyl or O) is a naturally occurring, genetically coded amino acid used by some methanogenic archaea and one known bacterium in enzymes that are part of their methane-producing metabolism. It is similar to lysine, but with an added pyrroline ring linked to the end of the lysine side chain."@en . . . .