Methanococcus jannaschii generates L-proline by cyclization of L-ornithine

Cell extracts of Methanococcus jannaschii have been shown to readily conver t L-ornithine to L-proline. This cyclization reaction proceeds with the los s of only the C-2 nitrogen, as has been documented for ornithine cyclodeami nase (EC 4.3.1.12). Since no gene homologous to that coding for ornithine c yclodeaminase is present in the genome of M. jannaschii, these results indi cate that proline biosynthesis in M. jannaschii is accomplished by a previo usly unrecognized enzyme.