Phytochem, Vol 23, Plenum Press, New York, pp.
This third method is used in Virtual Singer.
Among the reported SAM analogues, a selenium-based -adenosyl--selenomethionine (SeAM, 2) analogue, ProSeAM, has received recent interest because it stands as the SAM analogue containing the smallest bioorthogonal functionality (a propargyl group) and, more importantly, demonstrates broad compatibility toward native methyltransferases. ProSeAM is featured by its selenonium moiety, which is equivalent to the sulfonium of other SAM analogues. The replacement of sulfonium with selenonium for this cofactor was shown to be essential for the suppression of undesired decomposition of the propargylic handle to a ketone byproduct. Another chemical feature of -alkyl SeAM analogues lies in their weaker chalcogen-carbon bonds in comparison with the equivalent sulfonium analogues. -Alkyl SeAM analogues were thus expected to be more reactive as cofactors in methyltransferase-catalyzed transalkylation reactions, although this has yet to be demonstrated broadly for the various classes of methyltransferases.
A Nutritional Take on Traditional Drink Recipes
Several groups have shown that bulky -alkyl SAM analogues lacking sulfonium-β-sp1/sp2 carbons as activating groups are typically inert as methyltransferase cofactor surrogates. The rationale for this observation involves β-sp1- or β-sp2-carbon conjugative stabilization of the transition state during enzyme-catalyzed SN2 transalkylation reactions. Given the weaker carbon–chalcogen bonds of selenium-based analogues, it is of general interest to examine whether the chalcogen-β-sp1 or -sp2 functionality is dispensable for enzyme-mediated transalkylation reactions.
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7. Rapidity of onset of the antidepressant effect of parenteral S-adenosyl-L-methionine.
Fava M, Giannelli A, Rapisarda V, Patralia A, Guaraldi GP.
Depression Research Program, Massachusetts General Hospital,USA.
Psychiatry Res. 1995 Apr 28;56(3):295-7. PMID: 7568552 
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8. Double-blind, placebo-controlled study of S-adenosyl-L-methionine in depressed postmenopausal women.
Salmaggi P, Bressa GM, Nicchia G, Coniglio M, La Greca P, Le Grazie C.
Obstetrics and Gynecology Department, University La Sapienza School of Medicine, Rome, Italy.
Psychother Psychosom. 1993;59(1):34-40. PMID: 8441793