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B6db references: 91177884

type Journal Article
authors Forchhammer, K.; Bock, A.
title Selenocysteine synthase from Escherichia coli. Analysis of the reaction sequence
journal J Biol Chem
ui 91177884
year (1991)
volume 266
number 10
pages 6324-8.
keywords Autoradiography
abstract The product of the selA gene, selenocysteine synthase, is a pyridoxal 5- phosphate-containing enzyme which catalyzes the conversion of seryl- tRNA(Sec UCA) into selenocysteyl-tRNA(Sec UCA). Reduction of the aldimine group of pyridoxal 5-phosphate inactivates the enzyme. When reacted with seryl-tRNA(Sec UCA) as sole substrate, pyruvate (and possibly also ammonia) is released; in the presence of a high concentration of potassium borohydride, alanyl-tRNA(Sec UCA) is formed from seryl-tRNA(Sec UCA). These results support the notion that the formyl group of pyridoxal phosphate forms a Schiff base with the alpha- amino group of L-serine with the subsequent 2,3-elimination of a water molecule and the generation of an aminoacrylyl-tRNA(Sec UCA) intermediate. ATP is not required for this reaction step, but it is necessary for the conversion of aminoacrylyl-tRNA into selenocysteyl- tRNA(Sec UCA) which, in addition, requires the SELD protein and reduced selenium. Selenocysteine synthase forms a stable complex with seryl- tRNA(Sec UCA) with one tRNA molecule bound per two 50-kDa monomers. The enzyme does not interact with serine-inserting tRNA species. Taken together, the results show that biosynthesis of selenocysteine takes place in the enzyme-bound state and involves the dehydration of L- serine esterified to tRNA in a first step formally followed by the 2,3- addition of HSe- which is provided by the SELD protein in an ATP- dependent reaction in the form of a reactive selenium donor molecule.
last changed 2002/11/12 16:17

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