Stable isotope labeling is a standard technique for tracing material transfer in molecular, ecological and biogeochemical studies. The main assumption in this approach is that the enrichment with a heavy isotope has no effect on the organism metabolism and growth, which is not consistent with current theoretical and empirical knowledge on kinetic isotope effects. Here, we demonstrate profound c...

Nine isotopomers of tryptamine and its halogen derivatives, labeled with deuterium, tritium in side chain, i.e., [(1R)-2H]-, [(1R)-3H]-, 5-F-[(1R)-2H]-, 5-F-[(1R)-3H]-, 5-Br-[(1R)-2H]-, double labeled [(1R)-2H/3H]-, 5-F-[(1R)-2H/3H]-, and ring labeled [4-2H]-, and [5-2H]-tryptamine, were obtained by enzymatic decarboxylation of l-Trp and its appropriate derivatives in deuteriated or tritiated m...

With the intention to assist mechanistic studies of two-hydron-transfer reactions using lH/2H isotope effects we have carried out theoretical studies of the two-hydron-transfer reaction between formamidine molecules. The ab initio STO-3G potential energy surface has been calculated and all stationary points characterized by their force constant matrices. With this basis set the two hydrons are ...

Computational chemistry predicts that atomic motions on the femtosecond timescale are coupled to transition-state formation (barrier-crossing) in human purine nucleoside phosphorylase (PNP). The prediction is experimentally supported by slowed catalytic site chemistry in isotopically labeled PNP (13C, 15N, and 2H). However, other explanations are possible, including altered volume or bond polar...

To further validate the doubly labeled water method for measurement of CO2 production and energy expenditure in humans, we compared it with near-continuous respiratory gas exchange in nine healthy young adult males. Subjects were housed in a respiratory chamber for 4 days. Each received 2H2(18)O at either a low (n = 6) or a moderate (n = 3) isotope dose. Low and moderate doses produced initial ...

A novel diode laser spectrometer was developed using dualwavelength multiplexing, ensuring ideal conditions for high-precision and simultaneous measurements of the 2H/1H, 17O/16O, and 18O/16O isotope ratios in water. A 1.4-m diode laser probed a H16OH / HO2H line pair near 7198 cm-1, while a similar laser observed H16OH, H17OH, and H18OH rovibrational lines around 7183 cm-1, or a H16OH / H18OH ...

The use of stable isotope labeling has revolutionized NMR studies of nucleic acids, and there is a need for methods of incorporation of specific isotope labels to facilitate specific NMR experiments and applications. Enzymatic synthesis offers an efficient and flexible means to synthesize nucleoside triphosphates from a variety of commercially available specifically labeled precursors, permitti...

Stable isotope labeling is widely used to encode and quantify proteins in mass-spectrometry-based proteomics. We compared metabolic labeling with stable isotope labeling by amino acids in cell culture (SILAC) and chemical labeling by stable isotope dimethyl labeling and find that they have comparable accuracy and quantitative dynamic range in unfractionated proteome analyses and affinity pull-d...

Determining which proteins are unique among one or several protein populations is an often-encountered task in proteomics. To this purpose, we present a new method based on trypsin-catalyzed incorporation of the stabile isotope (18)O in the C-termini of tryptic peptides, followed by LC-MALDI MS analysis. The analytical strategy was designed such that proteins unique to a given population out of...