How Does Mass Spectrometry Accomplish Peptide Sequence Identification
The Principle and Process of Peptide Sequence Identification by Mass Spectrometry
1. Sample Preparation and Pre-treatment
Protein samples are initially subjected to enzymatic digestion to yield a collection of peptides. These peptides are subsequently purified and enriched to ensure compatibility with downstream mass spectrometric analysis.
2. Ionization Process
Prior to mass analysis, peptides are ionized using techniques such as Electrospray Ionization (ESI) or Matrix-Assisted Laser Desorption/Ionization (MALDI).
3. Mass Determination of Peptides
The ionized peptides are introduced into a mass analyzer—commonly a Time-of-Flight (TOF) or Ion Trap mass spectrometer—where their mass-to-charge (m/z) ratios are precisely measured.
4. Fragmentation
Following initial mass analysis, peptide ions undergo collision-induced dissociation (CID) in a collision cell, where they interact with inert gases such as nitrogen or noble gases to generate fragment ions.
5. Mass Determination of Fragments
The mass-to-charge ratios of the resulting fragment ions are determined. These data provide the basis for deducing the amino acid sequence of the original peptide.
6. Data Analysis and Peptide Sequence Identification
Mass spectrometry data analysis software, such as Mascot or SEQUEST, is employed to match the experimentally acquired peptide and fragment ion information against protein databases, thereby enabling the identification of the peptide sequence.
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