Methionine Cycle Analysis Service

Methionine (Met) is an essential amino acid. In the Methionine Cycle, methionine's methyl group becomes activated by ATP with the  addition of adenosine to the sulfur of methionine, adjacent to the  methyl group to form S−Adenosyl Methionine (SAMe). Removal of the methyl group from SAMe results in the formation of S−Adenosyl Homocysteine (SAH), which is  immediately converted to the amino acid homocysteine by removal of the adenosine molecule.  Homocysteine can then be modified in three different ways. In liver cells (and  only in liver cells) homocysteine can irreversibly enter the transsulfuration pathway  (catalyzed by Vitamin B6) to produce the amino acid cysteine. It has been estimated that 60% of homocysteine is metabolized by transsulfuration in the liver, with glucocorticoids increasing  that percentage. Cysteine can be incorporated into proteins, can be used in the  formation of the anti-oxidant molecule glutathione (GSH), or can be oxidized to form the amino acid taurine. If homocysteine does not enter the  transsulfuration pathway, it can be converted back to methionine by the  addition of a methyl group by one of two pathways. For one pathway of methyl  group addition, methionine  synthase enzyme catalyzes the transfer of a methyl group from  methylated folic acid (MTHF) to homocysteine assisted by vitamin B12,  which takes the methyl group from MTHF and adds it to the homocysteine. In another pathway (only in the liver), betaine (TMG) is the source  of the methyl group transferred to homocysteine.

Methionine Cycle Analysis Service

One of the metabolites in the methionine  cycle, S-adenosylmethionine (SAM), is the universal methyl donor and is the  substrate for a host of methyltransferases among which are the DNA  methyltransferases and histone methyltransferases that regulate gene silencing  and epigenetic inheritance. The level of SAM varies with methionine input and  folate status, and, together with its product S-adenosylhomocysteine (SAH), is  used as an indicator of methylation capacity. Another metabolite in the  methionine cycle is homocysteine, and elevated levels of homocysteine are  generally accepted as a major biomarker for cardiovascular disease. In  addition, via the cystathionine-β-synthase (CBS) reaction, the methionine cycle  provides the first step in the synthesis of reduced glutathione (GSH), a key  antioxidant.

The methionine cycle has three important  functions in cellular metabolism. First, it regulates the balance between  methionine and cysteine for protein synthesis; second, it provides the  substrate for polyamine synthesis, and third, it provides the mechanism by which  methyl groups are transferred from 5-methyltetrahydrofolate to a broad variety  of substrates and constitutes the primary mechanism for transmethylation  reactions in mammals. Normal functioning of the methionine cycle is essential  for growth and development, and defects in methionine metabolism are associated  with a variety of diseases ranging from cardiovascular disease to psychiatric  disorders, DNA methylation status and cancer.

Because of its central role in cell  metabolism, the operation of the methionine cycle has been the subject of  numerous experimental studies. Studies have revealed complex responses to  experimental variation in its various components. Some of this complexity  arises from the fact that enzymes of the methionine cycle are activated and  inhibited by several of the intermediates of the cycle. A significant part of  the complexity arises from nonlinearities in the interactions among the  components of the cycle that make the response to perturbation  context-dependent, and therefore non-intuitive and unpredictable. Much of what  is known about the properties and behavior of the pathway comes from a broad  body of empirical experience, both in vivo and in vitro.  By providing the  exact molecular weights and retention time, LC–MS/MS techniques serves as a  powerful analytical tool for identification and quantification of small  molecules (metabolites). Creative Proteomics has established sensitive,  reliable, and accurate HPLC-MS/MS method for quantification of metabolites in methionine cycle metabolites.



Sample Requirement


Methionine Cycle Metabolites Quantified in This Service

With integrated set of  separation, characterization, identification and quantification systems  featured with excellent robustness & reproducibility, high and  ultra-sensitivity, Creative Proteomics provides reliable, rapid and  cost-effective Methionine Cycle Metabolites targeted  metabolomics services.

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Ordering Procedure

* For Research Use Only. Not for use in diagnostic procedures.
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