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-   -   Net charge of a peptide Why is it +2 not +3 (Asp-Gly-Arg-His) at pH1? (http://www.molecularstation.com/forum/peptide-forum/85110-net-charge-peptide-why-2-not-3-asp-gly-arg-his-ph1.html)

Waffles 04-11-2012 06:40 AM

Net charge of a peptide Why is it +2 not +3 (Asp-Gly-Arg-His) at pH1?
 
I had this question on a quiz:
The overall charge of a peptide of the following peptide sequence at pH 1 would be (Asp-Gly-Arg-His)??

I though the answer was +3 but I was wrong, it is +2. Why?

This is what I thought, Where am I going wrong???
At PH1 the amino group with pka of about 9 would be +1
At PH1 the Arginine group with pka of about 12.5 would be +1
At PH1 the Histidine Side chain with pka of about 6 would be +1
At PH1 the carboxyl group with pka of about 2 would be 0

treebell23 04-11-2012 09:51 AM

How to find Rolloff Containers and Dumpster Space leases
 
There are an increasing number of people that will be choosing to deal with unwelcome solutions in an friendly to the environment fashion. It is important which when you are performing a cleanup to do it carefully so that you do not end up with incidents.

Kunal Pandya 05-24-2012 08:59 AM

Re: Net charge of a peptide Why is it +2 not +3 (Asp-Gly-Arg-His) at pH1?
 
I hope the peptide asked in your quiz is cyclic (i.e. amino of aspartic is covalently bound with carboxyl of Histidine) and if so then you loss +1 of amino group of aspartic so you remain with his and arg +1 so total charge on peptide is +2.

In general nomenclature peptide sequence written as Asp-Gly-Arg-His but in your question it written as (Asp-Gly-Arg-His) so may be it indicate that it have to cyclised but in that case questioner must have to write word cyclo also,but this is only explanation to explain charge +2.

Regards
Kunal pandya:hyper:


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