AJP - Endocrinology and Metabolism, Vol 263, Issue 4 E667-E675, Copyright © 1992 by American Physiological Society
Isotopomer spectral analysis of triglyceride fatty acid synthesis in 3T3-L1 cells
A. T. Kharroubi, T. M. Masterson, T. A. Aldaghlas, K. A. Kennedy and J. K. Kelleher
Department of Physiology, George Washington University Medical Center, Washington, District of Columbia 20037.
A new analysis of stable isotope data for biosynthesis reaction, isotopomer
spectral analysis (ISA), is demonstrated. ISA is theoretically applicable
for polymerization biosynthesis where data are collected using selected
ion-monitoring gas chromatography-mass spectrometry. ISA utilizes the
discrete spectrum of isotopomer abundances and the multinomial distribution
to estimate two key parameters related to the biosynthesis. These
parameters are 1) the dilution of the precursor immediately before
biosynthesis and 2) the dilution of the newly synthesized product in the
sampled compartment. Differentiated 3T3-L1 cells incorporated 2 mM
[1,2-13C]acetate into triglyceride palmitate, yielding a spectrum of mass
isotopomers of palmitate. The set of equations for the first nine
isotopomers were solved for the two parameters using nonlinear regression.
We found that precursor dilutions for acetate and glucose were constant
over time, whereas the product dilution parameter increased with time, as
expected for cells accumulating triglyceride palmitate. Mathematical
procedures are presented for calculating 1) the predicted isotopomer
fractional abundance values and 2) the correction for atoms other than the
tracer atom in the mass ion.
