| S-adenosylmethionine (SAM, AdoMet) is a biologically active molecule distributed in all body tissues and fluids. It is involved in a number of biochemical reactions such as transmethylation, thanssulfuration and polyamine synthesis. As a potential therapeutic agent, SAM is being used as the counter drug and nutrient supplement. SAM is produced by SAM synthetase, from ATP and methionine. Highly expressed SAM synthetase with the genetic engineering utilized for the production of SAM is one of hot spots of present SAM preparation research.In this study, the gene encoding S-adenosy-L-methionine synthetase (SAMS), from the genomic DNA of Saccharomyces cerevisiae, was amplified by polymerase chain reaction and inserted into the secreted expression vector pPIC9K to get recombinant plasmid. The plasmid recombined was integrated into Pichia pastoris GS115 genome by electroporation. Methanol was added to a final concentration of 0.5% for the expression of recombination protein every 24 hours to maintain induction. The molecular weight of the expression protein identified by SDS-PAGE was about 50 kDa which was larger than the theoretical molecular mass of SAMS, which maybe result from glycosylation in the process of the secretion. Then, the protein was preliminarily purified by saturated ammonium sulfate. The activity of the recombinant enzyme was measured using high-performance liquid chromatography (HPLC) by determining the production of the S-adenosyl-l-methionine (SAM) with the enzyme secreted. Comparing the activity of enzyme before and after methanol-induced, and after preliminary purification, it was showed that the activity of SAMS after purification was improved to 2.3 times as that before purification. So SAMS with biological activity was secreted successfully in Pichia pastoris GS115 for the first time. The results of present provided were basis for the further investigation on industrial product of SAM by secreted SAM synthetase.
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