| Summary: | � A key experiment in biomedical research is monitoring the expression of different proteins in order to detect changes that occur in biological systems under different experimental conditions. �The method that is most widely used is�the Western blot analysis.� While Western blot is a workhorse in laboratories studying protein expression and has several advantages, it also has a number of significant limitations.� In particular, the method is semi-quantitative with limited dynamic range.� Western blot focuses on a single protein per sample with only a small number of representative samples analyzed in an experiment.� New quantitative tools have been needed for some time to at least supplement, & possibly replace, the Western blot. Mass spectrometric methods have begun to compete with Western blot for routine quantitative analyses of proteins.� One of these methods is based on the tandem mass spectrometry technique of selected reaction monitoring (SRM), which is also called multiple reaction monitoring (MRM). �Selected reaction monitoring is actually an older tandem mass spectrometry technique, first described in the late 70s, that is widely utilized in the quantitative analysis of small molecules like drugs & metabolites.� The use of selected reaction monitoring for the quantitative analysis of proteins has a number of advantages.� Most importantly, it is fundamentally quantitative with a wide dynamic range.� The output of the analysis is a numerical result that can range over several orders of magnitude.� Other advantages include sufficient specificity & sensitivity to detect low abundance proteins in complex mixtures.� Finally, selected reaction monitoring can be multiplexed to allow the quantitative analysis of relatively large numbers of proteins in a single sample in a single experiment.� �� This Brief will explain both the theoretical & experimental details of the selected reaction monitoring experiment as it is applied to proteins.
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