The mechanism of the argininosuccinate lyase reaction has been probed by the measurement of the effects of isotopic substitution at the reaction centers. A primary deuterium isotope effect of 1.0 on both V and V/K is obtained with (2S,3R)-argininosuccinate-3-d, while a primary 15N isotope effect on V/K of 0.9964 +/- 0.0003 is observed. The 15N isotope effect on the equilibrium constant is 1.018...

Article is made available in accordance with the publisher's policy and may be subject to US copyright law. Please refer to the publisher's site for terms of use. The MIT Faculty has made this article openly available. Please share how this access benefits you. Your story matters. We investigate the isotope effect on the London penetration depth of a superconductor which measures n S /m * , the...

The sulfur isotope effect produced by sulfate reducing microbes is commonly used to trace biogeochemical cycles of sulfur and carbon in aquatic and sedimentary environments. To test the contribution of intracellular coupling between carbon and sulfur metabolisms to the overall magnitude of the sulfur isotope effect, this study compared sulfur isotope fractionations by mutants of Desulfovibrio v...

Heavy-enzyme isotope effects (15N-, 13C-, and 2H-labeled protein) explore mass-dependent vibrational modes linked to catalysis. Transition path-sampling (TPS) calculations have predicted femtosecond dynamic coupling at the catalytic site of human purine nucleoside phosphorylase (PNP). Coupling is observed in heavy PNPs, where slowed barrier crossing caused a normal heavy-enzyme isotope effect (...

The effects of pH, solvent isotope, and primary isotope replacement on substrate dehydrogenation by Rhodotorula gracilis d-amino acid oxidase were investigated. The rate constant for enzyme-FAD reduction by d-alanine increases approximately fourfold with pH, reflecting apparent pKa values of approximately 6 and approximately 8, and reaches plateaus at high and low pH. Such profiles are observed...

Archean sulfur mass-independent fractionation (S-MIF) has been widely recognized as one of the strongest indicators for the rise of atmospheric oxygen in the Early Proterozoic. A decade after its discovery, the wide-ranging implications of Archean sulfur MIF have been discussed extensively and despite a number of recent studies on the gas-phase chemistry of sulfur, no definite overall picture h...

Kinetic isotope effects (V/K) were measured with AMP nucleosidases isolated from Azotobacter vinelandii, from a Vmax mutant enzyme of A. vinelandii and from Escherichia coli. Specifically labeled AMP substrates were used to measure 3H secondary and 14C primary kinetic isotope effects on the N-glycosidic bond hydrolysis of AMP in the presence and absence of the allosteric activator, MgATP. Use o...

The measurement of a deuterium equilibrium isotope effect (EIE) for the aryl CH···Cl- interaction of anion receptor 1H/1D is reported. Computations corroborate the results of solution measurements for a small, normal EIE in the full complex (KaH/KaD = 1.019 ± 0.010). Interestingly, isotope effects involving fragments of the anion receptor (urea, aryl ring, etc.) are predicted to produce an inve...

We investigated the effects of 25Mg-Porphyrin-Fullerene nanoparticles, (25MgPMC16) smart ferroporphyrin nanoparticles, on PC12 cells exposed to oxygen-glucose deprivation/reperfusion. In order to explore its effect on cells under oxygen-glucose deprivation conditions, the cultures were pretreated with 25MgPMC16 24 hours prior to oxygen-glucose deprivation/reperfusion. To initiate the oxygen-glu...

RXJ0501.7–0359 is a new V ∼ 17mag eclipsing polar discovered during the ROSAT all-sky survey (RASS). Extensive follow-up observations at X-ray (pointed ROSAT PSPC and HRI observations) and optical (time-resolved photometry and spectroscopy) wavelengths were obtained which allowed us to determine a very precise orbital period and to provide constraints for the masses of the binary components and...