How does mass spectrometry determine the features of a protein?

Mass spectrometry determines the features of a protein primarily by analyzing the time of flight of ionized peptide fragments. In this process, proteins are first digested into smaller peptide fragments, which are then ionized, typically using methods such as electrospray ionization or matrix-assisted laser desorption/ionization (MALDI). Once ionized, these peptides are accelerated in an electric field, causing them to travel through a vacuum.

The key principle behind the technique is that ions of different masses will take different amounts of time to travel a specific distance in the mass spectrometer; this is known as the time-of-flight (TOF) principle. Heavier peptides will travel slower than lighter ones, allowing the mass spectrometer to determine the mass-to-charge ratio (m/z) of the ions. By measuring the time of flight, one can infer the mass of the peptide fragments. This mass information, combined with further analysis, can provide insights into the protein’s identity, structure, and post-translational modifications.

The other methods mentioned, such as thermal conductivity measurement, detection of color changes, or quantification of solubility, do not play a role in mass spectrometry for protein analysis and are therefore not relevant to this technique. The