Abstract
In this issue of Clinical Chemistry , Bondar and coworkers at the Mayo Clinic report on development of a quantitative liquid chromatography-tandem mass spectrometry (LC-MS/MS) assay for zinc-α2-glycoprotein (1). The assay described may be more notable for the approach employed rather than for the specific analyte. Unlike most current clinical laboratory assays of proteins, the approach used does not rely on the specificity of antibodies for capture and detection. Instead, the assay described by Bondar et al. cleaves the protein into small peptides by proteolysis with trypsin. By use of LC-MS/MS, one of the peptide fragments released from zinc-α2-glycoprotein is ratioed vs a stable isotope-labeled form of the same peptide. The method serves as an example of an approach to protein quantification that does not require specific antibody reagents and may be broadly applicable. The instrument used for this analysis, an LC-triple quadrupole mass spectrometer, is an increasingly common tool in the clinical laboratory. Its range of applications now includes routine assays for (a) detecting inborn errors of metabolism, (b) monitoring therapeutic drugs, and (c) quantifying steroid and thyroid hormones. The technology provides …
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