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Isotopic Ratio Outlier Analysis (IROA) is a stable isotopic labeling technique that utilizes the creation of distinct signatures in the molecules of a biological sample for identification and quantification. The technique can be used in either an unbiased (untargeted) or targeted metabolic profiling methodology by varying experimental design. The molecular contents of a cell are 'labeled' by replacing their entire carbon content with the stable carbon-13 () isotope, centered on either a 5% or 95% isotopic balance, in order to create unique, highly informative isotopic patterns. Previous methods of stable isotopic labeling relied on higher purity (typically 98-99% carbon-12) isotopic material which generate very weak (minimal) patterns. The use of randomly labeled, uniform isotopic abundance creates isotopic patterns (signatures) of such strength that they are easily detected and used, imparting many analytical advantages to the IROA method. When considering a stable isotope experiment, although many stable isotopes can be considered, it is important to use an isotope that exhibits minimal biological isotopic effect. The advantage of , which has only an 8% mass difference from , is that it is generally well tolerated by most cells. One advantage of the IROA protocol over other stable isotopic labeling techniques is that once the labeling step takes place all biologically derived molecules are distinguishable from artifacts (which are present at only natural abundance), and each peak has a signature of its origin, an M+1 for the sample (Figure: G-) and an M-1 for the sample (Figure: G-). The mass spectral scans from these pooled samples show the pairing of biological peaks allowing: 1) the removal of artifacts; and 2) the reinforced identification of the compounds the peaks represent because the distance between the paired peaks exactly corresponds to the number of carbons in the molecule. == Protocol == Since all molecules (biochemicals, proteins, RNA and DNA) are labeled by the IROA protocol (Figure: A, B, C and D) it can be used in all 'omic sciences, however biochemical profiling or metabolomics is an especially useful case. The natural abundance of carbon is approximately 98.9% and 1.1% . Because of this, during mass spectrometric analysis carbon-based molecules have both a monoisotopic peak and a second peak, the "M+1" peak, that is caused by the presence of the isotopes of not only , but also , , and others (Figure: H-NA). The key to IROA is that analysis is done using a specific mixture of and . One isotope is present at approximately 95% and the other at 5%. This the concentrated isotope's corresponding peak dominates the dilute isotope. (Figure: G - ), (Figure: G - ). 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Isotopic ratio outlier analysis」の詳細全文を読む スポンサード リンク
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