478529-67-8Relevant articles and documents
Formation of complex organic molecules in methanol and methanol-carbon monoxide ices exposed to ionizing radiation - A combined FTIR and reflectron time-of-flight mass spectrometry study
Maity, Surajit,Kaiser, Ralf I.,Jones, Brant M.
, p. 3081 - 3114 (2015/02/05)
The radiation induced chemical processing of methanol and methanol-carbon monoxide ices at 5.5 K exposed to ionizing radiation in the form of energetic electrons and subsequent temperature programmed desorption is reported in this study. The endogenous formation of complex organic molecules was monitored online and in situ via infrared spectroscopy in the solid state and post irradiation with temperature programmed desorption (TPD) using highly sensitive reflectron time-of-flight (ReTOF) mass spectrometry coupled with single photoionization at 10.49 eV. Infrared spectroscopic analysis of the processed ice systems resulted in the identification of simple molecules including the hydroxymethyl radical (CH2OH), formyl radical (HCO), methane (CH4), formaldehyde (H2CO), carbon dioxide (CO2), ethylene glycol (HOCH2CH2OH), glycolaldehyde (HOCH2CHO), methyl formate (HCOOCH3), and ketene (H2CCO). In addition, ReTOF mass spectrometry of subliming molecules following temperature programmed desorption definitely identified several closed shell C/H/O bearing organics including ketene (H2CCO), acetaldehyde (CH3COH), ethanol (C2H5OH), dimethyl ether (CH3OCH3), glyoxal (HCOCOH), glycolaldehyde (HOCH2CHO), ethene-1,2-diol (HOCHCHOH), ethylene glycol (HOCH2CH2OH), methoxy methanol (CH3OCH2OH) and glycerol (CH2OHCHOHCH2OH) in the processed ice systems. Additionally, an abundant amount of molecules yet to be specifically identified were observed sublimating from the irradiated ices including isomers with the formula C3H(x=4,6,8)O, C4H(x=8,10)O, C3H(x=4,6,8)O2, C4H(x=6,8)O2, C3H(x=4,6)O3, C4H8O3, C4H(x=4,6,8)O4, C5H(x=6,8)O4 and C5H(x=6,8)O5. The last group of molecules containing four to five oxygen atoms observed sublimating from the processed ice samples include an astrobiologically important class of sugars relevant to RNA, phospholipids and energy storage. Experiments are currently being designed to elucidate their chemical structure. In addition, several reaction pathways were identified in the irradiated ices of mixed isotopes based upon the results of both in situ FTIR analysis and TPD ReTOF gas phase analysis. In general, the results of this study provide crucial information on the formation of a variety of classes of organics including alcohols, ketones, aldehydes, esters, ethers, and sugars within the bulk ices upon exposure to ionizing radiation that are relevant to the molecular clouds within the interstellar medium.
Enzyme architecture: Remarkably similar transition states for triosephosphate isomerase-catalyzed reactions of the whole substrate and the substrate in pieces
Zhai, Xiang,Amyes, Tina L.,Richard, John P.
supporting information, p. 4145 - 4148 (2014/04/03)
Values of (kcat/Km)GAP for triosephosphate isomerase-catalyzed reactions of (R)-glyceraldehyde 3-phosphate and k catKHPiKGA for reactions of the substrate pieces glycolaldehyde and HPO32- have been determined for wild-type and the following TIM mutants: I172V, I172A, L232A, and P168A (TIM from Trypanosoma brucei brucei); a 208-TGAG for 208-YGGS loop 7 replacement mutant (L7RM, TIM from chicken muscle); and, Y208T, Y208S, Y208A, Y208F and S211A (yeast TIM). A superb linear logarithmic correlation, with slope of 1.04 ± 0.03, is observed between the kinetic parameters for wild-type and most mutant enzymes, with positive deviations for L232A and L7RM. The unit slope shows that most mutations result in an identical change in the activation barriers for the catalyzed reactions of whole substrate and substrate pieces, so that the two transition states are stabilized by similar interactions with the protein catalyst. This is consistent with a role for dianions as active spectators, which hold TIM in a catalytically active caged form.
Role of Lys-12 in catalysis by triosephosphate isomerase: A two-part substrate approach
Go, Maybelle K.,Koudelka, Astrid,Amyes, Tina L.,Richard, John P.
experimental part, p. 5377 - 5389 (2011/03/22)
We report that the K12G mutation in triosephosphate isomerase (TIM) from Saccharomyces cerevisiae results in (1) a ～50-fold increase in Km for the substrate glyceraldehyde 3-phosphate (GAP) and a 60-fold increase in Ki for competitive inhibition by the intermediate analogue 2-phosphoglycolate, resulting from the loss of stabilizing ground state interactions between the alkylammonium side chain of Lys-12 and the ligand phosphodianion group; (2) a 12000-fold decrease in kcat for isomerization of GAP, suggesting a tightening of interactions between the side chain of Lys-12 and the substrate on proceeding from the Michaelis complex to the transition state; and (3) a 6 - 105-fold decrease in k cat/Km, corresponding to a total 7.8 kcal/mol stabilization of the transition state by the cationic side chain of Lys-12. The yields of the four products of the K12G TIM-catalyzed isomerization of GAP in D2O were quantified as dihydroxyacetone phosphate (DHAP) (27%), [1(R)-2H]DHAP (23%), [2(R)-2H]GAP (31%), and methylglyoxal (18%) from an enzyme-ca alyzed elimination reaction. The K12G mutation has only a small effect on the relative yields of the three products of the transfer of a proton to the TIM-bound enediol(ate) intermediate in D2O, but it strongly favors catalysis of the elimination reaction to give methylglyoxal. The K12G mutation also results in a ≥14-fold decrease in kcat/K m for isomerization of bound glycolaldehyde (GA), although the dominant observed product of the mutant enzyme-catalyzed reaction of [1- 13C]GA in D2O is [1-13C,2,2-di-2H]GA from a nonspecific protein-catalyzed reaction. The observation that the K12G mutation results in a large decrease in kcat/Km for the reactions of both GAP and the neutral truncated substrate [1-13C]GA provides evidence for a stabilizing interaction between the cationic side chain of Lys-12 and the negative charge that develops at the enolate-like oxygen in the transition state for deprotonation of the sugar substrate ";piece";.
