A biotinylated acetyl-CoA carboxylase from the microaerophilic bacterium was partially purified and characterized. The approximate molecular mass of the native enzyme was estimated at 235 kDa by native PAGE. A single band corresponding to approximately 24 kDa was detected by SDS-PAGE, suggesting that the native enzyme is a multi-protein complex. The protein was isolated from the soluble fraction of the cell. Catalytic activity was acetyl-CoA-dependent and inhibited by avidin but unaffected by avidin pre-treated with excess biotin. The end-product of the reaction was identified as malonyl-CoA and the reaction was shown to be reversible by NMR spectroscopy. The activity of the enzyme was 0.29 μmol min (mg protein). The for bicarbonate was calculated at 0.73 μmol min (mg protein), and the affinity of the enzyme for this substrate was relatively low, with an apparent of 16.6 mM. These data provide the first evidence of a possible physiological role for the requirement of high levels of CO for growth of this bacterium.


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