High sensitivity quantitation of peptides by mass spectrometry
The instant invention provides an economical flow-through method for determining amount of target proteins in a sample. An antibody preparation (whether polyclonal or monoclonal, or any equivalent specific binding agent) is used to capture and thus enrich a specific monitor peptide (a specific peptide fragment of a protein to be quantitated in a proteolytic digest of a complex protein sample) and an internal standard peptide (the same chemical structure but including stable isotope labels). Upon elution into a suitable mass spectrometer, the natural (sample derived) and internal standard (isotope labeled) peptides are quantitated, and their measured abundance ratio used to calculate the abundance of the monitor peptide, and its parent protein, in the initial sample.
1. A method for quantifying the amount of an unlabeled analyte in a biological sample, comprising:
measuring the amount of the unlabeled analyte and two or more stable-isotopically labeled versions of said analyte in said biological sample by mass spectrometry,
wherein said two or more stable-isotopically labeled versions of said unlabeled analyte are present at different known concentration levels from each other and have isotopic masses that differ from each other and from the mass of the unlabeled analyte in a manner that can be distinguished by a mass spectrometer, either through direct measurement of molecular mass or through mass measurement of fragments,
wherein measurement of the known amount of said two or more stable-isotopically labeled versions of the analyte provides an internal standard curve and
wherein the amount of said unlabeled analyte in said sample is calculated by comparison to said standard curve.
2. The method of claim 1 , wherein three or more stable-isotopically labeled versions of said unlabeled analyte are present at different known concentration levels from each other and said labeled versions have isotopic masses that differ from each other and from the mass of the unlabeled analyte, and
wherein measurement of the known amount of said three or more stable-isotopically labeled versions of the analyte provides said internal standard curve.
3. The method of claim 2 , wherein three stable-isotopically labeled versions of said unlabeled analyte are present.
4. The method of claim 1 , wherein said analyte is a peptide.
5. The method of claim 4 , wherein said peptide is a fragment of a protein.
6. The method of claim 1 , wherein the concentration levels of said at least two or more stable-isotopically labeled versions of said analyte cover a ten-fold range of concentration.
7. The method of claim 1 , wherein said biological sample is a bodily fluid.
8. The method of claim 1 , wherein said biological sample is a proteolytic digest of a bodily fluid.