Purification and properties of an archaebacterial enzyme: citrate synthase from Sulfolobus solfataricus.

Citrate synthase from the thermoacidophilic archaebacterium Sulfolobus solfataricus was purified to homogeneity. The synthase is a dimer composed of subunits of Mr approximately equal to 40,000. The Km values of acetyl-CoA and oxalacetate are 7 microM and 20 microM, respectively. NADH (Ki = 3.5mM) and ATP (Ki = 0.36mM) are competitive inhibitors vs acetyl-CoA. The dimeric structure and the inhibition by nucleotides (ATP greater than NADH) correlate the archaebacterial enzyme to synthases from eukaryotes and Gram-positive eubacteria.