Efficient improvement on stability of sarcosine oxidase via poly-lysine modification on enzyme surface

A novel modification method was proposed for improving the stability of sarcosine oxidase. In this process, sarcosine oxidase surface was efficiently linked with poly-lysine (poly-Lys) covalently after activation with N-ethyl-N′-3-dimethylaminopropyl carbodiimide (EDC); the optimal conditions for this reaction were also investigated. The molar ratios of enzyme-COOH to EDC and enzyme-COOH to poly-Lys-NH2 were 1:2 and 1:50, respectively, while the optimal reaction pH was 7.0. The covalently binding of poly-Lys onto enzyme surface was confirmed by mass spectrum (MS) and Fourier transform infrared spectroscopy (FTIR). The catalytic kinetic parameters (Km and Vmax) of modified enzyme were determined as 47.94 mM and 0.157 μmol/min, respectively. Moreover, compared to the native enzyme, the pH, thermal and storage stabilities of modified sarcosine oxidase were significantly improved. More than 90% of initial activity of modified enzyme was maintained at a broad pH range from 5.0 to 10.0. Most activity of modified enzyme could be detected after being incubated at 60 °C for 10 min. The storage stability was enhanced ∼12-fold after being stored at 37 °C for 7 days. The novel modification was highly efficient for improving the stability of sarcosine oxidase and might be a good reference for other similar enzymes.