Amino Acid Counter

How to Use the Amino Acid Counter

1. Paste your protein sequence in single-letter amino acid code into the text box.
2. Alternatively upload a .txt or .fasta file — FASTA headers are stripped automatically.
3. Click Count Amino Acids.
4. Results show: total residues, unique amino acids found, full count and percentage per residue, and a breakdown by physicochemical group (hydrophobic, polar, charged, etc.).

About Amino Acid Composition Analysis

Amino acid composition analysis reveals the relative abundance of each of the 20 standard amino acids in a protein. This information is widely used in protein biochemistry for several purposes.

Knowing the composition helps estimate the isoelectric point (pI), hydrophobicity, charge at a given pH, and stability of a protein. For example, a high proportion of hydrophobic residues (Leu, Ile, Val, Phe, Met) often indicates a membrane protein or a protein with a hydrophobic core.

Composition analysis is also used in protein purification strategy selection, SDS-PAGE prediction, and determining which chromatography method (ion exchange, hydrophobic interaction) will work best.

Physicochemical Groups Explained

• Hydrophobic: A, V, I, L, M, F, W, P — tend to form the protein core away from water.
• Polar (uncharged): S, T, C, Y, N, Q — can form hydrogen bonds; often surface-exposed.
• Positively charged: K, R, H — carry positive charge at neutral pH; important for DNA binding and salt bridges.
• Negatively charged: D, E — carry negative charge at neutral pH; important for calcium binding and ionic interactions.
• Special: G (maximum flexibility), P (rigid, breaks helices).