Novel affinity purification of monomeric sarcosine oxidase expressed in Escherichia coli

An efficient affinity‐purification protocol for Bacillus monomeric sarcosine oxidase (SOX) expressed in Escherichia coli BL21 (DE3) was developed. 4‐Aminopyrrole‐2‐carboxylic acid was chosen as the affinity ligand, which was coupled with Sepharose CL 4B via spacers composed of epichlorohydrin and ethylenediamine. With the affinity medium, the purification process consisted of only one affinity chromatography step to capture monomeric SOX. The purified SOX was 94 and 96% pure when analyzed on an HPLC Vydac C₈ column and reducing SDS‐PAGE. Meanwhile, the recoveries of typical SOX activity and protein were 90.8 and 37.5%, respectively, which were higher than other reported traditional protocols. Reducing SDS‐PAGE analysis revealed that the enzyme was a single polypeptide with the mass of ∼46 kDa. The desorption constant K_d and theoretical maximum absorption Q_max were 35 μg/mL and 52.7 mg/g, respectively, in absorption analysis. All results indicated that the method would be of great potential for purifying monomeric SOX on an industrial scale.