Comparison of pathways for amino acid biosynthesis in archaebacteria using their genomic DNA sequences

Metabolic pathmays for synthesizing amino acids in 'i archaebacteria were compared on the basis of enzymes identified using their genomic DNA sequences. No essential difference was found between the set of enzymes identified for a heterotroph, Archeaoglobus fulgidus, and for those of two autotrophs, Methanococcus jannzashii and Methanobacterium thermoautotrophicum. It is likely that these three organisms are able to synthesize all the 20 types of amino acids found in proteins in essentially the same way. From the genomes of the other four heterotrophs, Pyrococcus abyssi, Pyrococcus sp. OT3, Thermoplasma volcanium, and Aeropyrum pernix, most of the genes coding for enzymes in the pathway for synthesizing histidine from 5-phosphoribosyl-1-pyrophosphate were missing, as were many other genes coding for enzymes in the pathways for synthesizing valine and leucine from pyruvate. The pathways for synthesizing aromatic residues from 3-phosphoglycerate seemed to be missing from P. OT3, while in T. volcanium the pathways starting from oxaloacetate were found to be significantly incomplete.