Upon closer inspection, the classical view of the synchronous relationship between tropospheric methane mixing ratio and Greenland temperature observed in ice samples reveals clearly discernable variations in the magnitude of this response during the Late Pleistocene (<50kyr BP). During the Holocene this relationship appears to decouple, indicating that other factors have modulated the methane ...

In biomolecules, bifurcated H-bonds typically involve the interaction of two donor protons with the two lone pairs of oxygen. Here, we present direct NMR evidence for a bifurcated H-bonding arrangement involving nitrogen as the acceptor atom. Specifically, the H-bond network comprises the Nδ1 atom of histidine and both the backbone N-H and side-chain Oγ-H of threonine within the conserved TXXH ...

The kinetic mechanism of the reaction of D-amino acid oxidase (EC 1.4.3.3) from Trigonopsis variabilis with [alpha-1H]- and [alpha-2H]phenylglycine has been determined. The pH dependence of Vmax is compatible with pKa values of approximately 8.1 and >9.5, the former of which is attributed to a base which should be deprotonated for efficient catalysis. The deuterium isotope effect on turnover is...

We have used the isotope dilution technique to study changes in the body composition of a migratory shorebird species (Red Knot, Calidris canutus) through an assessment of the amount of body water in it. Birds were quantitatively injected with a dose of water with elevated concentrations of 2H, (17)O, and (18)O. Thereafter, blood samples were taken and distilled. The resulting water samples wer...

The methylated metallocenes (MeCp),M with M = V, Cr, Mn, Co, Ni (1-5) were investigated by 'H and 'H NMR spectroscopy at natural abundance. The 2H NMR signals are narrower by a factor of up to 30 compared with the corresponding 'H NMR signals, thus establishing an inexpensive method and a general improvement of the NMR spectra of paramagnetic x-complexes. This has allowed the resolution of the ...

Environmental temperature affects water turnover and isotope fractionation by causing water evaporation from the body in mammals. This may lead to rearrangement of the water stable isotope equilibrium in body fluids. We propose an approach to detect possible variations in the isotope ratio in different body fluids on the basis of different homoeothermic adaptations in varying reproductive stage...

The kinetic mechanism of Pseudomonas cepacia salicylate hydroxylase has been examined by steady state initial rate measurements, and stopped flow and equilibrium studies. Results indicate that salicylate and NADH bind to the hydroxylase randomly. The enzyme is reduced and NAD+ is released. Oxygen subsequently binds to the reduced enzyme . substrate complex, leading to the production of hydroxyl...

Three-dimensional, triple resonance NMR techniques are described for measurement of two-bond (intraresidual) and three-bond (sequential) amide deuterium isotope effects on 13CR chemical shifts. Measurements were carried out for uniformly 15N and 13C labeled human ubiquitin equilibrated in a 50% H2O/50% D2O mixed solvent. The three-bond isotope shift, 3∆CR(ND), ranges from about 10-50 ppb, and, ...

In recent years stable isotopes of metallic and semi-metallic elements have become popular as tracers in studies of nutrition and metabolism. There are several recent reviews on the use of stable isotopes of the mineral elements (Janghorbani & Young, 1980; Janghorbani et af . 1985). The orientation of these reviews has tended toward neutron-activation analysis in conjunction with the faecal iso...

In recent years stable isotopes of metallic and semi-metallic elements have become popular as tracers in studies of nutrition and metabolism. There are several recent reviews on the use of stable isotopes of the mineral elements (Janghorbani & Young, 1980; Janghorbani et af . 1985). The orientation of these reviews has tended toward neutron-activation analysis in conjunction with the faecal iso...