Purification and Some Properties of Citrate Synthase from a Nitrite-Oxidizing Chemoautotroph, Nitrobacter agilis ATCC 14123

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Citrate (si)-synthase (citrate oxaloacetate-lyase, EC 4.1.3.7) was purified as an electrophoretically homogeneous protein from a nitrite-oxidizing chemoautotrophic bacterium, Nitrobacter agilis ATCC 14123. The molecular mass (M_r) of the native enzyme was estimated to be about 250,000 by gel filtration, whereas SDS-PAGE gave two bands with M_r values of 45,000 and 80,000,respectively, suggesting that the enzyme is a tetramer consisting of two different subunits (α : 45,000,β : 80,000). The isoelectric point of the enzyme was 5.4. The pH and temperature optima on the citrate synthase activity ware about 7.5-8.0 and 30-35℃, respectively. The citrate synthase was stable in the pH range of 6.0-9.0 and up to 55℃. The apparent K_m values for oxaloacetate and acetyl-CoA were about 27μM and 410μM, respectively. The activity of citrate synthase was not inhibited by ATP (1mM), NADH (1mM) or 2-oxoglutarate (10mM), but was strongly inhibited by SDS (1mM). Activation by metal ions was not observed.
公益社団法人日本生物工学会の論文
1994-01-25