PATHWAYS OF ARGININE-BIOSYNTHESIS IN EXTREME THERMOPHILIC ARCHAEBACTERIA AND EUBACTERIA

The pathway of arginine biosynthesis was investigated in two thermophilic eubacteria, Thermus aquaticus and Thermotoga maritima, and in two thermophilic archaeobacteria, Sulfolobus solfataricus and Pyrococcus furiosus. In the first three organisms, arginine biosynthesis proceeds via N-acetylated intermediates as in mesophilic micro-organisms. Only the enzymes catalysing the three last steps of the pathway could be detected in P. furiosus. The two eubacterial strains possess an ornithine acetyltransferase and are thus able to recycle the acetyl group from acetylornithine to glutamate. The archaeobacterium, S. solfataricus, uses the linear pathway in which the formation of ornithine is mediated by the hydrolytic enzyme acetylornithinase. Repression of enzyme synthesis by arginine was observed for most of the enzymes tested in T. aquaticus and S. solfataricus. Feedback inhibition by arginine was shown only in the ornithine acetyltransferase from T. aquaticus. This inhibition pattern is of interest since it would be the first example of control of arginine biosynthesis at this particular step. Data concerning the thermal stability of the arginine biosynthetic enzymes are presented.