Pyrrolysine is the largest amino acid known which is naturally occurring. It is encoded genetically by a nucleotide sequence that usually halts the translation of mRNA.
It is found in a bacterium and in few species of Archaea. It is just like the lysine but it is different in having pyrrole ring which is attached to the one end of the lysine amino acid.
In our body, pyrrolysine is produced by special transfer RNA and an enzyme called aminoacyl transfer RNA. This amino acid also forms a part of the genetic code.
In our body, it is incorporated into active sites of many enzymes for example methyltransferase. Here on this enzyme is rotated freely. It is incorporated during the process of translation into messenger RNA with the help of codon UAG. This amino acid has not been studied too much. There are not many known functions of it.
It contains three chiral centers which result in eight enantiomers, but only one of these is utilized. Pyrrolysine is a labile amino acid and it can easily be destroyed by heat and acid hydrolysis. This amino acid was also found to be involved in the methanogenesis. The methane today is the greenhouse gas which is quite powerful. Pyrrolysine is the twenty-second amino acid of proteinogenic type.