Purification and Properties of a Citrate Synthase form Nitrosomonas sp. TK794 and a Comparison with the Enzymes of Another Nitrifying Bacteria

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Citrate(si)-synthase (citrate oxaloacetate-lyase, EC 4.1.3.7) was purified as an electrophoretically homogeneous protein from an ammonia-oxidizing chemoautotrophic bacterium, Nitrosomonas sp. TK794,The molecular mass of the native enzyme was estimated to be about 287 kDa by gel filtration, whereas SDS-PAGE produced one band with M_r values of 44.7 kDa, suggesing that the enzyme is a hexamer consisting of identical subunits. The isoelectric point of the enzyme was 5.0. The pH and temperature optima for citrate synthase (CS) activity was about 7.5-8.0 and 40℃, respectively. The citrate synthase was stable over a pH range of 6.0-8.5 and up to 40℃. The apparent K_m values for oxaloacetate and acetyl-CoA were about 11 μM and 247 μM, respectively. The activity of the citrate synthase was not inhibited by ATP, NADH or 2-oxoglutarate at 5 mM, and was activated by potassium chloride at 0.1-100 mM. The N-terminal amino acid sequence of the enzyme protein was PPQDVATLSPGENKKTIELPILG.
社団法人日本生物工学会の論文
1995-01-25