کد مقاله | کد نشریه | سال انتشار | مقاله انگلیسی | نسخه تمام متن |
---|---|---|---|---|
1180584 | 962860 | 2008 | 9 صفحه PDF | دانلود رایگان |
![عکس صفحه اول مقاله: Effect of mutation of lysine-120, located at the entry to the active site of O-acetylserine sulfhydrylase-A from Salmonella typhimurium Effect of mutation of lysine-120, located at the entry to the active site of O-acetylserine sulfhydrylase-A from Salmonella typhimurium](/preview/png/1180584.png)
O-Acetylserine sulfhydrylase catalyzes the final step of the biosynthesis of l-cysteine, the replacement of the β-acetoxy group of O-acetyl-l-serine (OAS) by a thiol. The enzyme undergoes a conformational change to close the site upon formation of the external Schiff base (ESB) with OAS. Mutation of K120 to Q was predicted to destabilize the closed form of the ESB and decrease the rate. The K120Q mutant enzyme was prepared and characterized by UV-visible absorbance, fluorescence, visible CD, and 31P NMR spectral studies, as well as steady state and pre-steady state kinetic studies. Spectra suggest a shift in the tautomeric equilibrium toward the neutral enolimine and an increase in the rate of interconversion of the open and closed forms of the enzyme. A decrease in the rate of both half reactions likely reflects the stabilization of the ESB as a result of the increased rate of equilibration of the open and closed forms of the enzyme along the reaction pathway. Data suggest a role of K120 in helping to stabilize the closed conformation by participating in a new hydrogen bond to the backbone carbonyl of A231.
Journal: Biochimica et Biophysica Acta (BBA) - Proteins and Proteomics - Volume 1784, Issue 4, April 2008, Pages 629–637