1. What is Monoisotopic Mass?

The monoisotopic mass is the sum of the masses of the atoms in a molecule using the most abundant isotope for each element. For peptides, it's calculated by summing the masses of the amino acids and subtracting the mass of water molecules lost during peptide bond formation.

2. How Does the Calculator Work?

The calculator uses the formula:

Where:

• \( MM \) — Monoisotopic mass (Da)
• \( MW_{aa} \) — Monoisotopic mass of each amino acid (Da)
• \( length \) — Number of amino acids in the peptide
• 18.01056 — Mass of one water molecule (Da)

Explanation: Each peptide bond formation results in the loss of one water molecule (H₂O), hence we subtract 18.01056 Da for each bond.

3. Importance of Monoisotopic Mass

Details: Monoisotopic mass is crucial in mass spectrometry for peptide identification, proteomics research, and protein characterization. It provides the most precise mass measurement for theoretical calculations.

4. Using the Calculator

Tips: Enter the peptide sequence using single-letter amino acid codes (e.g., ACED). The sequence is case-insensitive. Only standard 20 amino acids are supported.

5. Frequently Asked Questions (FAQ)

Q1: What's the difference between monoisotopic and average mass?
A: Monoisotopic mass uses exact masses of the most abundant isotopes, while average mass accounts for natural isotope abundance.

Q2: Are modified amino acids supported?
A: This calculator only handles standard amino acids. For modified residues, specialized tools are needed.

Q3: How accurate is this calculation?
A: The calculation uses precise monoisotopic masses and is theoretically exact for the given sequence.

Q4: What about N-terminal or C-terminal modifications?
A: This calculator assumes standard peptide termini. For modified termini, additional mass adjustments would be needed.

Q5: Can I calculate mass for multiple peptides?
A: This calculator handles single peptide sequences. For multiple peptides, each should be calculated separately.