AJP - Endocrinology and Metabolism, Vol 263, Issue 5 E988-1001, Copyright © 1992 by American Physiological Society

ARTICLES

Mass isotopomer distribution analysis: a technique for measuring biosynthesis and turnover of polymers

M. K. Hellerstein and R. A. Neese
Department of Nutritional Sciences, University of California, Berkeley 94720.

Mass isotopomer distribution analysis (MIDA) is a technique for measuring biosynthesis and turnover of polymers in vivo. A stable isotopically enriched precursor is administered, and the relative abundances of different mass isotopomers in the polymer of interest are measured by mass spectrometry (MS). By comparison of statistical distributions predicted from the binomial or multinomial expansion to the pattern of excess isotopomer frequencies observed in the polymer, the enrichment of the biosynthetic precursor subunits (p) for newly synthesized polymers is calculated. MIDA thereby provides a solution to the problem of determining the isotope content in the actual precursor molecules that entered a particular polymeric product (the "true" precursor). The fraction of polymer molecules in a mixture that were newly synthesized during an isotopic experiment (fractional synthesis) can then be calculated. We describe some mathematical characteristics of MIDA and point out certain advantageous features. For example, mathematical estimates of p remain valid even if there does not exist a single anatomic or functional precursor pool. The interpretation of decay curves of endogenously labeled polymers may be improved by the use of higher mass isotopomers, which better fulfill the assumption of flash labeling. By combining fractional synthesis values with rate constants of decay, absolute endogenous synthesis rates can be calculated. Thus, by using probability logic combined with MS analysis, MIDA allows dynamic measurements to be made through analyses on a polymer alone during both isotopic incorporation and decay phases. The method has been applied to fatty acids, cholesterol, and glucose and is potentially applicable to nucleic acids, porphyrins, perhaps proteins, and many other classes of polymers.

This article has been cited by other articles:

				S. K. Chacko, A. L. Sunehag, S. Sharma, P. J. J. Sauer, and M. W. Haymond Measurement of gluconeogenesis using glucose fragments and mass spectrometry after ingestion of deuterium oxide J Appl Physiol, April 1, 2008; 104(4): 944 - 951. [Abstract] [Full Text] [PDF]

				A. A. M. W. van Kempen, S. N. van der Crabben, M. T. Ackermans, E. Endert, J. H. Kok, and H. P. Sauerwein Stimulation of gluconeogenesis by intravenous lipids in preterm infants: response depends on fatty acid profile Am J Physiol Endocrinol Metab, April 1, 2006; 290(4): E723 - E730. [Abstract] [Full Text] [PDF]

				S. M. Turner, E. J. Murphy, R. A. Neese, F. Antelo, T. Thomas, A. Agarwal, C. Go, and M. K. Hellerstein Measurement of TG synthesis and turnover in vivo by 2H2O incorporation into the glycerol moiety and application of MIDA Am J Physiol Endocrinol Metab, October 1, 2003; 285(4): E790 - E803. [Abstract] [Full Text] [PDF]

				R. E. Goldstein, L. Rossetti, B. A. J. Palmer, R. Liu, D. Massillon, M. Scott, D. Neal, P. Williams, B. Peeler, and A. D. Cherrington Effects of fasting and glucocorticoids on hepatic gluconeogenesis assessed using two independent methods in vivo Am J Physiol Endocrinol Metab, November 1, 2002; 283(5): E946 - E957. [Abstract] [Full Text] [PDF]