| Attributs | Valeurs |
|---|
| type
| |
| Is Part Of
| |
| Subject
| |
| Title
| - The Reaction of Yeast Cystathionine β-Synthase Is Rate-Limited by the Conversionof Aminoacrylate to Cystathionine
|
| has manifestation of work
| |
| related by
| |
| Author
| |
| Abstract
| - Our studies of the reaction mechanism of cystathionine β-synthase from Saccharomycescerevisiae (yeast) are facilitated by the spectroscopic properties of the pyridoxal phosphate coenzymethat forms a series of intermediates in the reaction of l-serine and l-homocysteine to form l-cystathionine.To characterize these reaction intermediates, we have carried out rapid-scanning stopped-flow and single-wavelength stopped-flow kinetic measurements under pre-steady-state conditions, as well as circulardichroism and fluorescence spectroscopy under steady-state conditions. We find that the gem-diamineand external aldimine of aminoacrylate are the primary intermediates in the forward half-reaction withl-serine and that the external aldimine of aminoacrylate or its complex with l-homocysteine is the primaryintermediate in the reverse half-reaction with l-cystathionine. The second forward half-reaction ofaminoacrylate with l-homocysteine is rapid. No primary kinetic isotope effect was obtained in the forwardhalf-reaction with l-serine. The results provide evidence (1) that the formation of the external aldimineof l-serine is faster than the formation of the aminoacrylate intermediate, (2) that aminoacrylate is formedby the concerted removal of the α-proton and the hydroxyl group of l-serine, and (3) that the rate of theoverall reaction is rate-limited by the conversion of aminoacrylate to l-cystathionine. We compare ourresults with cystathionine β-synthase with those of related investigations of tryptophan synthase andO-acetylserine sulfhydrylase.
|
| article type
| |
| is part of this journal
| |
