PYRIDINE DINUCLEOTIDE BIOSYNTHESIS IN ARCHAEBACTERIA - PRESENCE OF NMN ADENYLYLTRANSFERASE IN SULFOLOBUS-SOLFATARICUS

The enzyme NMN adenylyltransferase, leading to NAD synthesis, has been observed for the first time in soluble extracts from the extreme acid othermophilic archaeon Sulfolobus solfataricus. Comparison of its mole cular and kinetic properties with those of the enzyme isolated from pr okaryotes and eukaryotes revealed significant differences, knowledge o f which may contribute to the understanding of metabolic evolutionary mechanisms. The thermophilic enzyme shows a molecular mass of about 66 ,000 and an isoelectric point of 5.4. The K-m values for ATP, NMN and nicotinic acid mononucleotide are 0.08 mu M, 1.4 mu M and 17 mu M, res pectively. The enzyme shows a remarkable degree of thermophilicity, wi th an activation energy of 95 kJ/mol.