Algos Problem 4: Sequencing Peptides eg Antibiotics Flashcards
Sie analysieren ein lineares Peptids der Länge 5 mit dem Massenspektrometer.
Geben Sie (2) mögliche Gründe an, warum das experimentelle Spektrum anders sein kann als das theoretisch erwartete Spektrum.
**Posttranslationale Modifikationen: **
zB Phosphorylierungen, Glykosylierungen, Acetylierungen –> andere Peptidmasse –> Peaks, die nicht im theoretischen Spektrum erwartet werden.
**Ionization efficiency: **
The ionization process in mass spectrometry may not be 100% efficient for all peptides, leading to variations in signal intensities. Some peptides may ionize less efficiently, resulting in lower intensity peaks or no detection at all in the experimental spectrum.
Fragmentierung:
fehlende Spaltung (missing cleavage site)
b-, y- and their derivative ions from peptides
Isotopic variations:
Isotopes of elements, such as carbon, nitrogen, and hydrogen, can affect the peptide’s mass. While theoretical spectra typically consider average atomic masses, experimental spectra may show slight deviations due to the presence of specific isotopes, especially if the instrument used has high resolution capabilities.
Contaminants or impurities:
The experimental spectrum may contain signals from contaminants or impurities present in the sample. These can arise from various sources, including the sample preparation process or contamination within the mass spectrometer.
Sample degradation or chemical instability:
Peptides can undergo degradation or chemical changes during sample preparation, storage, or ionization in the mass spectrometer. These alterations can lead to the detection of unexpected fragments or modifications in the experimental spectrum.
Instrument limitations:
Mass spectrometers have certain limitations in terms of sensitivity, resolution, and mass accuracy. These limitations can result in imperfect detection and representation of the peptide masses, leading to differences between the experimental and theoretical spectra.
