875669-72-0Relevant academic research and scientific papers
Facile synthesis of tetrafluorotyrosine and its application in pH triggered membrane lysis
Wang, Fang,Qin, Luoheng,Wong, Patrick,Gao, Jianmin
, p. 236 - 239 (2011/03/21)
"Smart" peptides that lyse membranes in response to biological stimuli are of considerable interest. Herein, we report a facile synthesis of l-tetrafluorotyrosine (l-f4Y) and its utilization as a pH sensing element. The synthetic route affords
pH rate profiles of FnY356-R2s (n = 2, 3, 4) in Escherichia coli ribonucleotide reductase: Evidence that Y356 is a redox-active amino acid along the radical propagation pathway
Seyedsayamdost, Mohammad R.,Yee, Cyril S.,Reece, Steven Y.,Nocera, Daniel G.,Stubbe, JoAnne
, p. 1562 - 1568 (2007/10/03)
The Escherichia coli ribonucleotide reductase (RNR), composed of two subunits (R1 and R2), catalyzes the conversion of nucleotides to deoxynucleotides. Substrate reduction requires that a tyrosyl radical (Y 122?) in R2 generate a transient cysteinyl radical (C 439?) in R1 through a pathway thought to involve amino acid radical intermediates [Y122? → W48 → Y 356 within R2 to Y731 → Y730 → C 439 within R1]. To study this radical propagation process, we have synthesized R2 semisynthetically using intein technology and replaced Y 356 with a variety of fluorinated tyrosine analogues (2,3-F 2Y, 3,5-F2Y, 2,3,5-F3Y, 2,3,6-F3Y, and F4Y) that have been described and characterized in the accompanying paper. These fluorinated tyrosine derivatives have potentials that vary from -50 to +270 mV relative to tyrosine over the accessible pH range for RNR and pKas that range from 5.6 to 7.8. The pH rate profiles of deoxynucleotide production by these FnY356-R2s are reported. The results suggest that the rate-determining step can be changed from a physical step to the radical propagation step by altering the reduction potential of Y356? using these analogues. As the difference in potential of the FnY? relative to Y? becomes >80 mV, the activity of RNR becomes inhibited, and by 200 mV, RNR activity is no longer detectable. These studies support the model that Y356 is a redox-active amino acid on the radical-propagation pathway. On the basis of our previous studies with 3-NO2Y356-R2, we assume that 2,3,5-F3Y356,2,3,6-F3Y356, and F4Y356-R2s are all deprotonated at pH > 7.5. We show that they all efficiently initiate nucleotide reduction. If this assumption is correct, then a hydrogen-bonding pathway between W48 and Y 356 of R2 and Y731 of R1 does not play a central role in triggering radical initiation nor is hydrogen-atom transfer between these residues obligatory for radical propagation.
Kinetic analysis of a protein tyrosine kinase reaction transition state in the forward and reverse directions
Kim, Kyonghee,Cole, Philip A.
, p. 6851 - 6858 (2007/10/03)
Protein tyrosine kinases catalyze the transfer of the γ-phosphoryl group from ATP to tyrosine residues in proteins and are important enzymes in cell signal transduction. We have investigated the catalytic phosphoryl transfer transition state of a protein tyrosine kinase reaction catalyzed by Csk by analyzing a series of fluorotyrosine-containing peptide substrates. It was established for five such fluorotyrosine-containing peptide substrates that there is good agreement between the tyrosine analogue phenol pK(a) and the ionizable group responsible for the basic limb of a pH rate profile analysis. This indicates that the substrate tyrosine phenol must be neutral to be enzymatically active. Taken together with previous data indicating a small β(nucleophile) coefficient (0-0.1), these results strongly support a dissociative transition state for phosphoryl transfer. In addition, the β(leaving group) coefficient was measured for the reverse protein tyrosine kinase reaction and shown to be -0.3. This value is in good agreement with a previously reported nonenzymatic model phosphoryl transfer reaction carried out under acidic conditions (pH 4) and is most readily explained by a transition state with significant proton transfer to the departing phenol.
