Mechanism
Sarcosine dehydrogenase, with sarcosine as its substrate, follows Michaelis-Menten kinetics and has a Km of 0.5 mM and a Vmax of 16 mmol/hr/mg protein. The enzyme is inhibited competitively by methoxyacetic acid, which has a Ki of 0.26 mM
The exact mechanism of sarcosine dehydrogenase is not available. However, according to the overall net reaction discussed in Honova.E, et al. paper:
- Sarcosine + H2O + O2 → glycine + formaldehyde + H2O2
the first step of the reaction might involve the transfer of a hydride on the N-methyl group of sarcosine onto FAD, allowing H2O to attack the carbocation in order to form intermediate 1 (See figure 1). There is no deamination step. Instead, the demethylation of the N-methyl group on sarcosine occurs directly. The reduced FADH- from the first step then is oxidized by O2 to form H2O2.
The demethylation of sarcosine catalyzed by sarcosine dehydrogenase can proceed with or without the presence of tetrahydrofolate. Under anaerobic condition and without tetrahydrofolate, however, a free formaldehyde is formed after the N-demethylation of sarcosine. The reaction with 1 mole of sarcosine and 1 mole of FAD, under this condition, yields 1 mole of glycine and 1 mole of formaldehyde (See figure 2 for mechanism).
Under the presence of tetrahydrofolate, sarcosine dehydrogenase binds to tetrahydrofolate and convert tetrahydrofolate to 5,10-methylenetetrahydrofolate. Tetrahydrofolate here serves as a 1-carbon acceptor during the demethylation process (See figure 3 for mechanism).
Read more about this topic: Sarcosine Dehydrogenase
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