Kharroubi A T, Masterson T M, Aldaghlas T A, Kennedy K A, Kelleher J K
Department of Physiology, George Washington University Medical Center, Washington, District of Columbia 20037.
Am J Physiol. 1992 Oct;263(4 Pt 1):E667-75. doi: 10.1152/ajpendo.1992.263.4.E667.
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.
本文展示了一种用于生物合成反应的稳定同位素数据的新分析方法——同位素异构体光谱分析（ISA）。ISA理论上适用于聚合生物合成，其中数据是使用选择离子监测气相色谱 - 质谱法收集的。ISA利用同位素异构体丰度的离散光谱和多项分布来估计与生物合成相关的两个关键参数。这些参数是：1）生物合成前体的稀释度，以及2）在采样隔室中新合成产物的稀释度。分化的3T3 - L1细胞将2 mM [1,2 - 13C]乙酸盐掺入甘油三酯棕榈酸酯中，产生了棕榈酸酯的一系列质量同位素异构体。使用非线性回归求解前九个同位素异构体的方程组以获得这两个参数。我们发现，乙酸盐和葡萄糖的前体稀释度随时间保持恒定，而产物稀释参数随时间增加，这与积累甘油三酯棕榈酸酯的细胞预期一致。本文还介绍了用于计算1）预测的同位素异构体分数丰度值和2）质量离子中示踪原子以外的原子校正的数学程序。
