Accelerator Mass Spectrometry (AMS) precisely quantifies zeptomoles to femtomoles of long lived isotopes, such as 14C, used as molecular labels in metabolic studies of nutrients, toxins, hormones, and therapeutics in hosts ranging from large animals (e.g. elephants), through human volunteers, model species, down to cells. In most cases, the compound of interest is labeled with the isotope prior to exposure at relevant environmental or physiologic concentrations. The dose produces radiologic exposures that are much lower than normal backgrounds, allowing metabolic studies in special populations such as women of child-bearing age and even children. The low natural background of long-lived isotopes provides sufficient sensitivity for tracing metabolites for months after a single dose of retained compounds. All metabolites are relatively quantified by their distinct isotopic content after chromatographic separations without requiring prior identification or synthesis of internal standards. Examples drawn from human nutrition and toxicology will be given. A new thrust at our laboratory will investigate metabolites in single selected yeast cells. An entire organisms can be uniformly labeled with the isotope so that seperable components of metabolic pathways can be quantified. AMS technology and availability will also be briefly discussed.

This work was performed in part under the auspices of the U.S. Department of Energy by University of California Lawrence Livermore National Laboratory under Contract No. W-7405-Eng-48, and supported in part by NIH NCRR-13461.