# Issue with submitting peptide with N-terminal Cys using CYF code

**URL:** <https://ask.bioexcel.eu/t/issue-with-submitting-peptide-with-n-terminal-cys-using-cyf-code/4843>\
**Category:** HADDOCK\
**Created:** [February 16, 2024, 5:07pm UTC](https://ask.bioexcel.eu/t/issue-with-submitting-peptide-with-n-terminal-cys-using-cyf-code/4843 "2024-02-16T17:07:27Z")\
**Posts on this page:** 2\
**Page:** 1

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**Author:** ![asd](https://avatars.discourse-cdn.com/v4/letter/a/c68b51/32.png) [@asd](https://ask.bioexcel.eu/u/asd)\
**Post date:** [February 16, 2024, 5:07pm UTC](https://ask.bioexcel.eu/t/issue-with-submitting-peptide-with-n-terminal-cys-using-cyf-code/4843/1 "2024-02-16T17:07:27Z")

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The HADDOCK category is meant to discuss any HADDOCK-related issue. For general information about HADDOCK refer to [HADDOCK – Bonvin Lab](http://www.bonvinlab.org/software/haddock2.4)  
Hi,

The software is amazing, thank you!  
Is there any way I can submit a peptide with N-terminal cysteine with the sulphur of the side chain coordinating to an iron? The problem is when I use the code CYF instead of CYS the N-terminal amine group only has one instead of two hydrogens.

Thank you!

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**Author:** ![amjjbonvin](https://dub1.discourse-cdn.com/flex013/user_avatar/ask.bioexcel.eu/amjjbonvin/32/23_2.png) [@amjjbonvin](https://ask.bioexcel.eu/u/amjjbonvin)\
**Post date:** [February 16, 2024, 7:03pm UTC](https://ask.bioexcel.eu/t/issue-with-submitting-peptide-with-n-terminal-cys-using-cyf-code/4843/2 "2024-02-16T19:03:07Z")

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The default is indeed uncharged termini because often the termini in a structure are the not real ones (e.g. density is missing).

You can make the N-ter charged if you wish (will then be -NH3+). For this you need expert access.