{"id":4110,"date":"2026-10-11T06:37:05","date_gmt":"2026-10-11T06:37:05","guid":{"rendered":"https:\/\/nhdbio.com\/?page_id=4110"},"modified":"2026-10-11T07:41:08","modified_gmt":"2026-10-11T07:41:08","slug":"%e8%82%bd%e6%9c%ab%e7%ab%af%e4%b9%99%e9%85%b0%e5%8c%96%e4%b8%8e%e9%85%b0%e8%83%ba%e5%8c%96","status":"publish","type":"page","link":"https:\/\/nhdbio.com\/cn\/analytical-methods\/peptide-terminal-acetylation-amidation\/","title":{"rendered":"\u591a\u80bd\u4e59\u9170\u5316\u4e0e\u9170\u80fa\u5316\uff1a\u4e24\u7aef\u5404\u6709\u4ec0\u4e48\u53d8\u5316\uff1f"},"content":{"rendered":"

Two labels show the same peptide sequence, but one also says \u201cAc\u201d or \u201camide.\u201d Are the products identical? Those small additions describe changes to the ends of the chain. They belong in both the specification and the expected mass.<\/p>\n

A peptide has a beginning and an end<\/h2>\n

A peptide sequence is usually written from its amino end, called the N-terminus, to its carboxyl end, called the C-terminus. Changing a group at either end can change the molecule without changing the sequence letters.<\/p>\n

The diagram shows a simplified end-group change, rather than a three-dimensional structure.<\/p>\n

\"Figure
Figure 1. N-terminal acetylation changes the group at the start of the chain.<\/figcaption><\/figure>\n

What does N-terminal acetylation add?<\/h2>\n

Compared with the corresponding free end, the net added composition is C2H2O. Its monoisotopic mass contribution is +42.010565 Da.<\/p>\n

State the location as well as the modification. A +42 shift alone does not tell you whether the acetyl group is at the N-terminus or another suitable position.<\/p>\n

Why C-terminal amidation makes the mass slightly lower<\/h2>\n

In a simplified picture, the C-terminal COOH group becomes CONH2. That replacement changes the atoms; it is not simply adding an extra group on top. The monoisotopic mass change is \u22120.984016 Da.<\/p>\n

Keep the minus sign. If your reference uses average molecular mass, use the matching average-mass calculation instead.<\/p>\n

\"Figure
Figure 2. C-terminal amidation changes COOH to CONH2.<\/figcaption><\/figure>\n

What happens when both ends change?<\/h2>\n

Start with an example unmodified monoisotopic mass of 1,000.000000 Da. Add 42.010565 for N-terminal acetylation and subtract 0.984016 for C-terminal amidation. The result is 1,041.026549 Da, with the rest of the molecule unchanged.<\/p>\n

This calculation predicts a mass difference. It does not predict the biological effect or stability of those changes.<\/p>\n

What is the result if the same example receives only C-terminal amidation?<\/strong><\/p>\n
\nSee the answer<\/summary>\n

1,000.000000 \u2212 0.984016 = 999.015984 Da.<\/p>\n<\/details>\n<\/div>\n

Acetylation is different from acetate<\/h2>\n

Acetylation means an acetyl group is covalently attached to the molecule. Acetate describes a salt component, or counterion, associated with the material. A label saying acetate does not by itself mean the peptide was N-terminally acetylated.<\/p>\n

Write the sequence, N- and C-terminal groups, other modifications and salt form as separate details.<\/p>\n

\"Figure
Figure 3. Acetylation and an acetate counterion are different specifications.<\/figcaption><\/figure>\n

Checking Thymosin \u03b11 or KPV forms<\/h2>\n

For Thymosin \u03b11 or KPV, check the actual end groups of the selected variant. Keep them with the sequence when requesting or comparing materials.<\/p>\n

Thymosin \u03b11<\/a> \/ KPV<\/a><\/p>\n

Discuss material and document requirements with NHD<\/a> \u00b7 Continue with the analytical guide<\/a><\/p>\n