|
type |
Journal Article |
authors |
Forchhammer, K.; Bock, A. |
title |
Selenocysteine synthase from Escherichia coli. Analysis of the reaction sequence |
journal |
J Biol Chem |
Activity |
2.9.1.1 |
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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