Application of mass isotopomer analysis for determination of pathways of glycogen synthesis.

An elementary exposition of the application of mass spectroscopy to studies with substrates labeled uniformly with 13C is presented. A procedure to obtain mass isotopomer spectra, corrected for natural abundance, of products labeled with 13C in several positions is outlined. The calculation for enrichment, a term equivalent to specific activity with radioisotopes, is shown. Examples of mass isotopomer patterns of blood glucose and glycogen are presented, and calculations of the contribution of the direct path to hepatic glycogen synthesis and the dilution of glucose-derived pyruvate are shown. The analysis of mass isotopomer patterns recently offered by C. Des Rosiers, B. R. Landau, and H. Brunengraber [Am. J. Physiol. 259 (Endocrinol. Metab. 22): E757-E762, 1990] is critically examined.