No abstract

No abstract

The utility and power of 3H NMR spectroscopy as a technique for monitoring biological systems in vivo is illustrated with glucose metabolism in erythrocytes. Use of C-1-tritiated glucose allowed us to monitor the disappearance of the a and P tritons, with the production of lactate and 'H3HO (HTO), as well as some intermediates. Spin lattice relaxation times (T,) were measured to avoid T, distortion of the spectral intensities. Detection of the formation of 1 mM tritiated water in the presence of 110 M H20 protons and deuterons allows the eventual fate of the label in the pentose shunt to be observed in vivo.3H NMR Spectroscopy. In these and earlier studies using rat erythrocytes (1-3) we have found 3H NMR spectroscopy to be a powerful technique for the study of metabolic pathways in vivo. The results that will be presented show that 3H has many advantages as an isotopic label and that NMR spectroscopy is able to follow the progress of this label through metabolic intermediates.Most isotopic studies of complex metabolic pathways rely on radioisotope counting methods that trade specificity for sensitivity-i.e., they measure total isotope concentration at some stage of an experiment. 3H is increasingly popular as a radiolabel due to its high specific activity (4)-i.e., 461 times that of 14C. This means tritiated substrates may be detected at much lower chemical concentrations than 14C-labeled radiochemicals, and the half-life of tritium is sufficiently long so as not to interfere with the study at hand.The nuclei most widely studied by NMR spectroscopy are 'H, 13C, and 31p, with 19F, 15N, and a number of quadrupolar nuclei such as 2H, 23Na, and 39K utilized to a lesser extent (5).In comparison with radioisotope methods, the NMR experiment maintains a high level of molecular specificity, but this strength is mitigated by the relative lack of sensitivity of the technique. Very few nuclei are suitable as isotopic tracers in biological NMR spectroscopy: 13C and 2H are the most commonly used. Tritium is both an NMR and a radioactive tracer. As an NMR nucleus 3H has all of the advantages of 1H: spin 1/2, high gyromagnetic ratio (y), and similar chemical shifts and couplings (4, 6). The absence of naturally occurring 3H (<10-16% of H isotopes) avoids confusion with regard to possible sources of the NMR signal, and with an appropriate choice of the labeling site the 3H atom is not subject to easy exchange.The analysis of 3H spectra is very similar to standard 1H

No abstract