Methylation plays a vital role in biological systems. SAM (S-adenosyl-L-methionine), an abundant cofactor in life, acts as a methyl donor in most biological methylation reactions. SAM-dependent methyltransferases (MTase) transfer a methyl group from SAM to substrates, thereby altering their physicochemical properties or biological activities. In recent years, many SAM analogues with alternative methyl substituents have been synthesized and applied to methyltransferases that specifically transfer different groups to the substrates. These include functional groups for labeling experiments and novel alkyl modifications. This review summarizes the recent progress in the synthesis and application of SAM methyl analogues and prospects for future research directions in this field.
S-Adenosylmethionine/metabolism* ; Methionine ; Methyltransferases/metabolism* ; Methylation ; Racemethionine

S-adenosyl-l-methionine (SAM) is ubiquitous in living organisms and plays important roles in transmethylation, transsulfuration and transamination in organisms. Due to its important physiological functions, production of SAM has attracted increasing attentions. Currently, researches on SAM production mainly focus on microbial fermentation, which is more cost-effective than that of the chemical synthesis and the enzyme catalysis, thus easier to achieve commercial production. With the rapid growth in SAM demand, interests in improving SAM production by developing SAM hyper-producing microorganisms aroused. The main strategies for improving SAM productivity of microorganisms include conventional breeding and metabolic engineering. This review summarizes the recent research progress in improving microbial SAM productivity to facilitate further improving SAM productivity. The bottlenecks in SAM biosynthesis and the solutions were also addressed.
S-Adenosylmethionine/metabolism* ; Plant Breeding ; Fermentation ; Metabolic Engineering

To utilize Pichia pastoris to produce S-adenosyl-L-methionine (SAM), an intracellular expression vector harboring S. cerevisiae SAM2 was transformed into GS115. A recombinant strain having 2 copies of expression cassette was obtained through G418 resistance screening. This strain had higher SAM synthetase activity and higher SAM production capacity than the original strain, when cultured in medium containing methanol and methionine. The carbon source and nitrogen source of medium was optimized. The results showed SAM production by this strain was closely related to carbon metabolism. With supplementation of 0.2% glycerol every day from the beginning of 3rd day, this strain produced 1.58 g/L SAM when cultured in a medium containing 0.75% L-methionine and optimized carbon and nitrogen source after 6 days.
Methionine Adenosyltransferase ; genetics ; metabolism ; Pichia ; genetics ; Recombinant Proteins ; metabolism ; S-Adenosylmethionine ; biosynthesis

The yield of S-adenosyl-L-methionine (SAM) on high-cell-density fermentation by saccharomyces cerevisiae is mostly affected by the feeding strategy of pre-L-methionine. The mutant strain SAM0801 that could accumulate more SAM was used in this study. Six high-cell-density fermentation experiments in 5 L fermentor were investigated to get the optimal feeding time and amount of L-methionine. The results showed that when 40 g L-methionine was added in the fermentor after 30 h fermentation, a dry cell weight of 100 g/L was achieved. Under this condition, after 58 h fermentation, both the dry cell weight and the yield of SAM reached the maximum, 168 g/L and 14.48 g/L respectively.
Bioreactors ; microbiology ; Fermentation ; Methionine ; analysis ; metabolism ; Mutation ; S-Adenosylmethionine ; biosynthesis ; Saccharomyces cerevisiae ; genetics ; growth & development ; metabolism

We investigated the effects of dietary folate supplementation on plasma homocysteine, vitamin B12 and hepatic levels of S-adenosylmethionine (SAM) and S-adenosylhomocysteine (SAH) in diet-induced hyperhomocysteinemic rats. All animals were fed 0.3% homocysteine diet for 2 weeks, then they were placed either on a 0.3% homocystine or no homocystine with or without 8 mg/kg folate diet for 8 weeks. Homocystine diet induced hyperhomocysteinemia up to 3.5-fold at 10 weeks (28.0+/-4.8 micromol/l vs. 7.9+/-0.3 micromol/l). Dietary folate supplementation caused a significant decrease in plasma homocysteine levels which had been increased by a homocystine-diet. Also, dietary folate supplementation made them return to control levels at 4 wk when the diet was free of homocystine. Plasma folate levels were markedly decreased with homocystine diet with no folate supplementation. Plasma vitamin B12 did not differ between groups. Dietary homocystine increased hepatic levels of SAM in folate supplementation group at 10 weeks (p<0.05). Dietary folate supplementation increased hepatic levels of SAM/SAH ratios in homocystine group (p<0.05). In conclusion, dietary folate supplementation can effectively ameliorate the detrimental effects of hyperhomocysteinemia.mia.
Animals ; Diet ; Folic Acid* ; Homocysteine ; Homocystine* ; Hyperhomocysteinemia* ; Metabolism* ; Plasma ; Rats* ; S-Adenosylhomocysteine ; S-Adenosylmethionine* ; Vitamin B 12

The yield of S-adenosyl-L-methionine (SAM) by saccharomyces cerevisiae fermentation was affected by the strategy of feeding L-methionine. The effects that feeding strategies and the amount of precursor L-methionine had on the production of SAM by saccharomyces cerevisiae G14 were investigated. The results showed that feeding L-methionine could obviously improve the accumulation of SAM, and both the biomass and SAM yield relied heavily on different feeding strategies. In our work, it was found that total amount of L-methionine added should be no less than 0.7g per 10 grams of dry cell weight. Five different feeding strategies had been investigated in our experiment, and such comparison indicated that favorable results could be achieved as the biomass reached the status of high cell density (120g/L). If 9 grams of the precursor L-methionine was introduced once and for all, the accumulation of SAM reached maximum of 4.31g/L at the 18th hour after addition; if the precursor amino acid was fed at a rate of 2g/h in 5 h, maximum yield of 4.98g/L was achieved at the 28th hour after feeding. Thus high cell density fermentation can be successfully applied to SAM production by Saccharomyces cerevisiae with the consequence of over 130g/L of biomass gained using the above two strategies.
Bioreactors ; microbiology ; Cell Culture Techniques ; methods ; Culture Media ; Fermentation ; Methionine ; metabolism ; S-Adenosylmethionine ; biosynthesis ; Saccharomyces cerevisiae ; growth & development ; metabolism

OBJECTIVETo observe the therapeutic effects of S-Adenosyl-L-methionine(SAMe) in the treatment of cholestasis after total parenteral nutrition (TPN).

METHODSThirty SD rats were randomly divided into control group, hypercalorie group, hypercalorie adds SAMe group; sepsis group and sepsis adds SAMe group; their stages of cholestasis were compared. Sixteen patients received SAMe because of cholestasis after prolonged TPN.

RESULTSBile flow, serum levels of total bile acid and gamma-glutamyl transpeptidase were elevated markedly in hypercalorie and sepsis groups. Hepatocellular fatty degeneration, dilatation of cholangiole, and bile sludge could be seen microscopically, while SAMe administration in hypercalorie adds SAMe and sepsis adds SAMe groups could increase bile flow, decrease serum total bile acid and gamma-glutamyl transpeptidase levels. Microscopic findings were normal, no dilated cholangiole or bile sludge could be found. Cholestasis and abnormal results of liver function test were the main clinical manifestations of 16 patients before SAMe administration. Three weeks after SAMe administration, their serum levels of total bilirubin, alkaline phosphotase, gamma-glutamyl transpeptidase, alanine aminotransferase(ALT), and aspartate aminotransferase(AST) were decreased markedly; they became normal in the 4 th week.

CONCLUSIONSAMe could prevent and treat cholestasis without discontinuation of TPN.

Adult ; Animals ; Cholestasis ; drug therapy ; metabolism ; pathology ; Female ; Humans ; Liver ; pathology ; Male ; Middle Aged ; Parenteral Nutrition, Total ; adverse effects ; Rats ; Rats, Sprague-Dawley ; S-Adenosylmethionine ; therapeutic use

Alterations in sulfur amino acid metabolism are associated with an increased risk of a number of common late-life diseases, which raises the possibility that metabolism of sulfur amino acids may change with age. The present study was conducted to understand the age-related changes in hepatic metabolism of sulfur amino acids in 2-, 6-, 18- and 30-month-old male C57BL/6 mice. For this purpose, metabolite profiling of sulfur amino acids from methionine to taurine or glutathione (GSH) was performed. The levels of sulfur amino acids and their metabolites were not significantly different among 2-, 6- and 18-month-old mice, except for plasma GSH and hepatic homocysteine. Plasma total GSH and hepatic total homocysteine levels were significantly higher in 2-month-old mice than those in the other age groups. In contrast, 30-month-old mice exhibited increased hepatic methionine and cysteine, compared with all other groups, but decreased hepatic S-adenosylmethionine (SAM), S-adenosylhomocysteine and homocysteine, relative to 2-month-old mice. No differences in hepatic reduced GSH, GSH disulfide, or taurine were observed. The hepatic changes in homocysteine and cysteine may be attributed to upregulation of cystathionine β-synthase and down-regulation of γ-glutamylcysteine ligase in the aged mice. The elevation of hepatic cysteine levels may be involved in the maintenance of hepatic GSH levels. The opposite changes of methionine and SAM suggest that the regulatory role of SAM in hepatic sulfur amino acid metabolism may be impaired in 30-month-old mice.
Aging ; Amino Acids, Sulfur ; Animals ; Child, Preschool ; Cystathionine ; Cysteine ; Down-Regulation ; Glutathione ; Homocysteine ; Humans ; Infant ; Male* ; Metabolism* ; Metabolomics ; Methionine ; Mice* ; Plasma ; S-Adenosylhomocysteine ; S-Adenosylmethionine ; Sulfur* ; Taurine ; Up-Regulation

Elevated plasma homocysteine ( Hcy) is a risk factor for cognitive dysfunction and Alzheimer disease, although the mechanism is still unknown. Both folate and betaine, a choline metabolite, play essential roles in the remethylation of Hcy to methionine. Choline deficiency may be associated with low folate status and high plasma Hcy. Alterations in DNA methylation also have established critical roles for methylation in development of the nervous system. This study was un-dertaken to assess the effect of choline and folate deficiency on Hcy metabolism and genomic DNA methylation status of the liver and brain. Groups of adult male Sprague Dawley rats were fed on a control, choline-deficient ( CD) , folate-deficient ( FD) or choline/folate-deficient ( CFD) diets for 8 weeks. FD resulted in a significantly lower hepatic folate ( 23%)(p < 0.001) and brain folate ( 69%)(p < 0.05) compared to the control group. However, plasma and brain folate remained unaltered by CD and hepatic folate reduced to 85% of the control by CD ( p < 0.05) . Plasma Hcy was signi-ficantly increased by FD ( 18.34 +/- 1.62 micrometer) and CFD ( 19.35 +/-3.62 micrometer) compared to the control ( 6.29 +/-0.60 micrometer) ( p < 0.001) , but remained unaltered by CD. FD depressed S-adenosylmethionine ( SAM) by 59% ( p < 0.001) and ele-vated S-adenosylhomocysteine ( SAH) by 47% in liver compared to the control group ( p < 0.001) . In contrast, brain SAM levels remained unaltered in CD, FD and CFD rats. Genomic DNA methylation status was reduced by FD in liver ( p< 0.05) . Genomic DNA hypomethylation was also observed in brain by CD, FD and CFD although it was not signifi-cantly different from the control group. Genomic DNA methylation status was correlated with folate stores in liver ( r = - 0.397, p < 0.05) and brain ( r = - 0.390, p < 0.05) , respectively. In conclusion, our data demonstrated that genomic DNA methylation and SAM level were reduced by folate deficiency in liver, but not in brain, and correlated with folate concentration in the tissue. The fact that folate deficiency had differential effects on SAM, SAH and genomic DNA methylation in liver and brain suggests that the Hcy metabolism and DNA methylation are regulated in tissue-specific ways.
Adult ; Alzheimer Disease ; Animals ; Betaine ; Brain ; Choline ; Choline Deficiency ; Diet ; DNA Methylation* ; DNA* ; Folic Acid ; Homocysteine* ; Humans ; Liver ; Male ; Metabolism ; Methionine ; Methylation ; Nervous System ; Plasma* ; Rats* ; Rats, Sprague-Dawley ; Risk Factors ; S-Adenosylhomocysteine ; S-Adenosylmethionine

OBJECTIVE: Recent epidermiologic studies suggested that alterations in folate metabolism as a result of polymorphism in the enzyme 5,10-methylenetetrahydrofolate reductase(MTHFR) have been frequently associated with neural tube defects, vascular disease, and some cancers. A common 677C->T polymorphism in the MTHFR gene results in thermolability and reduced MTHFR activity that decreases the pool of 5-methyltetrahydrofolate and increases the pool of 5,10-methylenetetrahydrofolate. A possible cause underlying altered DNA methylation could be an insufficient level of S-adenosylmethionine as a consequence of weaker alleles of MTHFR gene. Therefore, the weak MTHFR activity may underlie susceptibility to brain neoplasms. We now report the associations of MTHFR polymorphisms in three groups of adult brain tumors: gliomas, meningiomas and schwannomas. METHODS: We analyzed DNA of 71 brain tumors and 254 age- and sex-matched controls with a case-control study. MTHFR variant alleles were determined by a PCR-restriction fragment length polymorphism assay. RESULTS: The incidence of the MTHFR 677TT genotype was higher among 20 schwannoma cases compared with that of 254 controls, conferring a 5-fold increase of the risk of schwannomas(odds ratio, OR=4.75 ; 95% confidence index, CI=1.05-21.50). The homozygous mutant group had half the risk of meningioma(OR=0.42:95% CI = 0.11-1.58) compared with the homozygous normal or heterozygous genotypes. There was no significant difference in MTHFR 677TT genotype frequency between glioma group(19 cases) and control group(254 cases)(OR = 1.53 ; 95% CI = 0.30-7.73). CONCLUSION: The data indicate that the homozygous 677TT MTHFR genotype confers the significantly higher risk of schwannoma and the lower risk of meningioma. However, our study had limited a statistical power because of the small sample size, which is reflected in the wide CIs. Hence, these findings need to be confirmed in larger populations.
Adult ; Alleles ; Brain Neoplasms* ; Brain* ; Case-Control Studies ; DNA ; DNA Methylation ; Folic Acid ; Genotype ; Glioma ; Humans ; Incidence ; Meningioma ; Metabolism ; Methylenetetrahydrofolate Reductase (NADPH2) ; Neural Tube Defects ; Neurilemmoma ; Oxidoreductases* ; Risk Factors ; S-Adenosylmethionine ; Sample Size ; Vascular Diseases