[Enhancement of the production of SAM by overexpression of SAM synthetase in Pichia pastoris].

S-Adenosyl-L-methionine(SAM) is an important metabolic intermediate in the metabolic flux of sulphur. SAM is involved in three key metabolic pathways: transmethylation, transsulfuration and polyamine synthesis. As a potential therapeutic agent, SAM is being used as over the counter drug and nutrient supplement. An expression vector, harboring SAM synthetase 2 gene from S. cerevisiae and regulated by the glyceraldehyde-3-phosphate dehydrogenase gene promoter P(GAP), was transformed into GS115 strain of P. pastoris. Through zeocin resistance and expression screening, a recombinant strain was obtained that had high SAM yield and the fermentation conditions were optimized. The results showed that carbon source, nitrogen source, pH and dissolved oxygen had significant effects on the accumulation of SAM. The SAM production of the recombinant cells reached 2.49 g/L after fermentation for three days under the optimized conditions. The present studies show that fermentation of recombinant P. pastoris strain, expressing heterologous SAM synthetase gene, may be a promising approach for the production of SAM.