Study on Characterizations of Immobilized S-adenosylmethionine Synthetase on Chitosan Microspheres

S-adenosylmethionine(SAM) synthetase was expressed in E. coli,and then the purified SAM synthetase was immobilized on chitosan microspheres with glutaraldehyde crosslinking.Properties of the immobilized enzyme were identified. The results showed the optimal conditions for the immobilization of the enzyme were as follows:the mass fraction of chitosan was 2.5%;the volume fraction of glutaraldehyde was 0.8%;the amount of enzyme was 6 mg/mL gel;the immobilization time was 12 hours. Under these conditions,the activity yield of the immobilized enzyme was 76%. The immobilized enzyme showed a good stability compared with the free enzyme.After incubation at 55 ℃ for 5 h the immobilized enzyme maintained 53% of the original activity while the free enzyme lost all activity at 50 ℃ for 5 h. The immobilized enzyme also showed a good stability in alkaline solution. It still kept more than 80% of the original activity when incubated in the buffer of pH 7.5~9.0 at 4 ℃ for 10 h. The immobilized enzyme was employed to synthesize the SAM and it remained 64% activity after five times repeated operations. The substrate conversion rate was more than 95% in the presence of 30 mmol/L adenosine triphosphate(ATP)。