20283-52-7Relevant articles and documents
Acid-Base Catalysis of the Elimination and Isomerization Reaction of Triose Phosphates
Richard, John P.
, p. 4926 - 4936 (1984)
The nonenzymatic β-elimination, isomerization, and racemization reactions of L-glyceraldehyde 3-phosphate (LGAP) are through a common enediolate intermediate which partitions between leaving group expulsion, C-1 protonation, and C-2 protonation, respectively.The elimination reaction mechanisms of LGAP and dihydroxyacetone phosphate (DHAP) are Elcb because enolate intermediates have been identified in very closely related systems.Strong general base catalysis of elimination demontstrates that the enediolate intermediate is formed essentially irreversibly by rate-determinig substrate deprotonation.The pH rate profile for the elimination of LGAP is first order in hydroxide at pH > 10 due to direct substrate deprotonation by hydroxide, pH independent at pH 6-10 due to intramolecular deprotonation by the C-3 phosphate dianion, and first order in hydroxide at pH 0.2 M concentrations of 3-oxo- and 3-hydroxy-substituted quinuclidine buffers there is a curvature in buffer catalysis plots for the elimination reaction of DHAP which is attributed to a change from rate determining substrate deprotonation to partially rate determining leaving group expulsion.The isomerization and racemization reactions of LGAP were followed by coupling the formation of DHAP andDGAP to enzymatic NADH oxidation under conditions where > 90percent of the product is from the elimination reaction.Uncatalyzed racemization is five times slower than uncatalyzed isomerization, and buffer-catalyzed racemization is estimated to be > 20 times slower than buffer-catalyzed isomerization.The observed rate constant for LGAP isomerization is second order in total buffer concentration; the basic form of buffer acts to increase the steady-state concentration of the enediolate, and the acidic form of the buffer increases the fractional partitioning of the enediolate to DHAP.Rate constant ratios kBH/ke and k-o/ke for partitioning of the enediolate between buffer-catalyzed or uncatalyzed protonation (kBH or k-o) and leaving group expulsion (ke) were obtained from the slopes and the intercepts respectively of linear plots of the isomerization/elimination rate constant ratio against buffer concentration.The Bronsted α value for enediolate protonation at C-1 is 0.47.The (kBH/ke)H2O/(kBD/ke)D2O ratio for quinuclidinonium catalysis in H2O and D2O is 3.2.The pH dependence plot of kBH/ke values shows pH-independent regions at pH 10, with a 100-fold greater limiting kBH/ke value at pH > 10.The increased kBH/Ke value at high pH is due to slower leaving group expulsion from the enediolate phosphate dianion compared to that of the enediolate phosphate monoanion.The nonenzymatic reactions of triose ...
Prebiotic synthesis of aminooxazoline-5′-phosphates in water by oxidative phosphorylation
Fernández-García,Grefenstette,Powner
supporting information, p. 4919 - 4921 (2017/07/11)
RNA is essential to all life on Earth and is the leading candidate for the first biopolymer of life. Aminooxazolines have recently emerged as key prebiotic ribonucleotide precursors, and here we develop a novel strategy for aminooxazoline-5′-phosphate synthesis in water from prebiotic feedstocks. Oxidation of acrolein delivers glycidaldehyde (90%), which directs a regioselective phosphorylation in water and specifically affords 5′-phosphorylated nucleotide precursors in upto 36% yield. We also demonstrated a generational link between proteinogenic amino acids (Met, Glu, Gln) and nucleotide synthesis.
Structural mutations that probe the interactions between the catalytic and dianion activation sites of triosephosphate isomerase
Zhai, Xiang,Amyes, Tina L.,Wierenga, Rik K.,Loria, J. Patrick,Richard, John P.
, p. 5928 - 5940 (2013/09/23)
Triosephosphate isomerase (TIM) catalyzes the isomerization of dihydroxyacetone phosphate to form d-glyceraldehyde 3-phosphate. The effects of two structural mutations in TIM on the kinetic parameters for catalysis of the reaction of the truncated substrate glycolaldehyde (GA) and the activation of this reaction by phosphite dianion are reported. The P168A mutation results in similar 50- and 80-fold decreases in (kcat/Km)E and (kcat/Km)E·HPi, respectively, for deprotonation of GA catalyzed by free TIM and by the TIM·HPO 32- complex. The mutation has little effect on the observed and intrinsic phosphite dianion binding energy or the magnitude of phosphite dianion activation of TIM for catalysis of deprotonation of GA. A loop 7 replacement mutant (L7RM) of TIM from chicken muscle was prepared by substitution of the archaeal sequence 208-TGAG with 208-YGGS. L7RM exhibits a 25-fold decrease in (kcat/Km)E and a larger 170-fold decrease in (kcat/Km)E·HPi for reactions of GA. The mutation has little effect on the observed and intrinsic phosphodianion binding energy and only a modest effect on phosphite dianion activation of TIM. The observation that both the P168A and loop 7 replacement mutations affect mainly the kinetic parameters for TIM-catalyzed deprotonation but result in much smaller changes in the parameters for enzyme activation by phosphite dianion provides support for the conclusion that catalysis of proton transfer and dianion activation of TIM take place at separate, weakly interacting, sites in the protein catalyst.
