1. What is Peptide Exact Mass?

The peptide exact mass is the calculated mass of a peptide based on the sum of the isotopic masses of its constituent atoms minus the mass of water molecules lost during peptide bond formation.

2. How Does the Calculator Work?

The calculator uses the formula:

Where:

• \(\sum(\text{Isotopic Masses})\) — Sum of the isotopic masses of all atoms in the peptide
• \(\text{Water}\) — 18.015 unified atomic mass units (u), representing the mass of water lost per peptide bond

Explanation: Each peptide bond formation results in the loss of one water molecule (H₂O), which must be accounted for in the mass calculation.

3. Importance of Exact Mass Calculation

Details: Exact mass calculations are essential for mass spectrometry analysis, peptide identification, and quantitative proteomics studies.

4. Using the Calculator

Tips: Enter the sum of isotopic masses in unified atomic mass units (u). The value must be greater than 0.

5. Frequently Asked Questions (FAQ)

Q1: Why subtract water mass?
A: During peptide bond formation, a water molecule is lost for each bond created between amino acids.

Q2: What are typical peptide masses?
A: Small peptides range from a few hundred to several thousand u, while proteins can be much larger.

Q3: How accurate is this calculation?
A: The calculation is theoretically exact, but actual measurements may vary due to isotopic distributions.

Q4: What about post-translational modifications?
A: Modifications like phosphorylation or glycosylation require additional mass adjustments.

Q5: Can this be used for protein mass calculation?
A: Yes, the same principle applies, though proteins typically have more complex isotopic distributions.