Biosynthesis, selenomethionine

FIG. 1 Biosynthesis of selenomethionine adapted from Marschner (1995) Schrauzer (2000). 

Blau, M. 1961. Biosynthesis of (75Se)selenomethionine and (75Se)selenocystine. Biochem. Biophys. Acta 49, 389-390. 

Tuve, T. and Williams, H.H. 1961. Metabolism of selenium by Escherichia coli biosynthesis of selenomethionine. J. Biol. Chem. 236, 597-601. 

L. Hinojosa Reyes, F. Moreno Sanz, P. Herrero Espilez, J. M. Marchante-Gayon, J. I. Garcia Alonso, A. Sanz-Medel, Biosynthesis of isotopically enriched selenomethionine application to its accurate determination in selenium-enriched yeast by isotope dilution analysis-HPLC-ICP-MS, J. Anal. Atom. Spectrom., 19 (2004), 1230-1235. 

The biosynthesis of the seleno amino acids is not fully understood. It seems, however, that selenite and selenate are reduced to hydrogen selenide, which reacts with L-serine or L-homoserine as described for hydrogen sulfide (Dll and D 12). L-Methylselenocysteine and L-selenomethionine may be formed by methyl group transfer. 

The specificity of human 5 -methylthioadenosine phosphorylase is rather strict if compared with that of the enzyme purified from E. coli The replacement of the sulfur atom of 5 -methylthioade-nosine by selenium and the replacement of the methyl group by an ethyl one are the only substrate modifications compatible with enzymic activity. The rate of breakdown of 5 -methylselenoadenosine equals that of 5 -methylthioadenosine (see Fig. 8). This finding agrees with the generally accepted view that the enzyme systems that normally utilize sulfur metabolites also convert their selenium analogues, i.e. the interchangeability of methionine and selenomethionine has been demonstrated in protein synthesisas well as that of S-adenosylmethionine and Se-adenosylselenomethionine in polyamine biosynthesis. 

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