GLUTAMATE-1-SEMIALDEHYDE AMINOTRANSFERASE FROM SULFOLOBUS-SOLFATARICUS

Glutamate-1-semialdehyde aminotransferase (GSA-AT) from the extremely thermophilic bacterium Sulfolobus solfataricus has been purified to ho mogeneity and characterized. GSA-AT is the last enzyme in the C-5 path way for the conversion of glutamate into the tetrapyrrole precursor de lta-aminolaevulinate (ALA) in plants, algae and several bacteria. The active form of GSA-AT from S. solfataricus seems to be a homodimer wit h a molecular mass of 87 kDa. The absorption spectrum of the purified aminotransferase is indicative of the presence of pyridoxamine 5'-phos phate (PMP) cofactor, and the catalytic activity of the enzyme is furt her stimulated by addition of PMP. 3-Amino-2,3-dihydrobenzoic acid is an inhibitor of the aminotransferase activity. The N-terminal amino ac id sequence of GSA-AT from S. solfataricus was found to share signific ant similarity with the eukaryotic and eubacterial enzymes. Evidence i s provided that ALA synthesis in S. solfataricus follows the C-5 pathw ay characteristic of plants, algae, cyanobacteria and many other bacte ria.