Abstract
The enzyme NMN adenylyltransferase, leading to NAD synthesis, has been observed for the first time in soluble extracts from the extreme acidothermophilic archaeon Sulfolobus solfataricus. Comparison of its molecular and kinetic properties with those of the enzyme isolated from prokaryotes and eukaryotes revealed significant differences, knowledge of 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 μM, 1.4 μM and 17 μM, respectively. The enzyme shows a remarkable degree of thermophilicity, with an activation energy of 95 kJ/mol.
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