Amino acid biosynthesis in the halophilic archaeon Haloarcula hispanica

Biosynthesis of proteinogenic amino acids in the extremely halophilic archa eon Haloarcula hispanica was explored by using biosynthetically directed fr actional C-13 labeling with a mixture of 90% unlabeled and 10% uniformly C- 13-labeled glycerol, The resulting C-13-labeling patterns in the amino acid s were analyzed by two-dimensional C-13,H-1 correlation spectroscopy. The e xperimental data provided evidence fur a split pathway for isoleucine biosy nthesis, with 56% of the total Ile originating from threonine and pyruvate via the threonine pathway and 44% originating from pyruvate and acetyl coen zyme A via the pyruvate pathway. In addition, the diaminopimelate pathway i nvolving diaminopimelate dehydrogenase was shown to lead to lysine biosynth esis and an analysis of the C-13-labeling pattern in tyrosine indicated nov el biosynthetic pathways that have so far not been further characterized. F or the 17 other proteinogenic amino acids, the data were consistent with da ta for commonly found biosynthetic pathways. A comparison of our data with the amino acid metabolisms of eucarya and bacteria supports the theory that pathways for synthesis of proteinogenic amino acids were established befor e ancient cells diverged into archaea, bacteria, and eucarya.