The dynamic range of plasma protein abundance, ranging from milligrams to picograms per milliliter, makes characterization of this proteome nearly impossible with current analytical methods. Plasma preprocessing by high-abundance protein depletion may concomitantly remove important diagnostic information. This article describes an original chromatographic procedure to isolate proteins bound to human serum albumin (HSA). Using HSA as an "affinity agent", we significantly improved the detection and identification of HSA ligands by two-dimensional liquid chromatography tandem mass spectrometry (2D LC-MS/MS). Some of the characterized species were not previously reported in published blood databases. Albumin-binding proteins may be classified as belonging to several putative functional categories and span a wide variety of predicted physiological functions.
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