Go Back   Science Forums Biology Forum Molecular Biology Forum Physics Chemistry Forum > Molecular Research Topics Forum > Proteomics Forum > Peptide Forum
Register Search Today's Posts Mark Forums Read

Peptide Forum Peptide Forum. Ask and discuss questions on peptide protocols, custom peptide synthesis, peptide identification and peptide sequencing.


How do I calculate the overall charge of the peptide 'Asp-His-Arg' at various pHs?

How do I calculate the overall charge of the peptide 'Asp-His-Arg' at various pHs? - Peptide Forum

How do I calculate the overall charge of the peptide 'Asp-His-Arg' at various pHs? - Peptide Forum. Ask and discuss questions on peptide protocols, custom peptide synthesis, peptide identification and peptide sequencing.


Reply
 
LinkBack Thread Tools Display Modes
  #1  
Old 10-30-2012, 06:16 PM
Joe Joe is offline
Pipette Filler
Points: 184, Level: 3 Points: 184, Level: 3 Points: 184, Level: 3
Activity: 0% Activity: 0% Activity: 0%
 
Join Date: Oct 2008
Posts: 11
Thanks: 0
Thanked 0 Times in 0 Posts
Default How do I calculate the overall charge of the peptide 'Asp-His-Arg' at various pHs?



I have been given the following table of the pKa associated with each ionizable group in the peptide 'Asp-His-Arg'

Asp: pKa NH3+: 9.9, pKa COOH: 2.0, pKa Side Chain: 3.9
His: pKa NH3+: 9.3, pKa COOH: 1.8, pKa Side Chain: 6.0
Arg: pKa NH3+: 9.0, pKa COOH: 1.8, pKa Side Chain: 12.5

I have worked out the overall charge to be +1 at pH 7 (though this could be incorrect), but have now been asked to calculate the overall charge at pHs: 1.8, 6, 7, 9.9

How do I do this?? Any help would be greatly appreciated, thanks.
Reply With Quote
  #2  
Old 11-02-2012, 04:55 AM
Kunal Pandya's Avatar
Graduate Student
Points: 3,203, Level: 37 Points: 3,203, Level: 37 Points: 3,203, Level: 37
Activity: 0% Activity: 0% Activity: 0%
 
Join Date: Dec 2009
Location: India
Posts: 141
Thanks: 0
Thanked 6 Times in 6 Posts
Smile Re: How do I calculate the overall charge of the peptide 'Asp-His-Arg' at various pHs

When pH is equal to pKa value then half of the carboxyl group get deprotonated result in -0.5 charge and when pH is greater then pKa value of COOH result in generation of -1 charge (COO- generate which have -1 charge)

When pH is equal to pKa value then half of the amino group get deprotonated result in + 0.5 charge and when pH is greater pKa value of NH3+ result in loss of +1 charge (NH2 generate which have zero charge)

Now your sequence is NH2-Asp-His-Arg-COOH

So Asp having one NH2 group while one caroxyl functionality in side chain
His having one imidazole group functionality in side chain
Arg having one COOH group while Guanidine functionality in side chain

So now you can easily calulate charge on peptide at various pH


At pH 1.8 = Asp amino group having +1 charge while carboxyl Zero
His side chain group posses +1 charge
Arg Side chain posses +1 charge while carboxyl group having -0.5 charge
Total charge = +1+0+1+1-0.5 = + 2.5

At pH 6 = Asp amino group having +1 charge while carboxyl having -1 charge
His side chain group posses + 0.5 charge (Half group get deprotonated)
Arg Side chain posses +1 charge while carboxyl group having -1 charge
Total charge = +1-1+0.5+1-1 = + 0.5


At pH 7 = Asp amino group having +1 charge while carboxyl having -1 charge
His side chain group posses 0 charge
Arg Side chain posses +1 charge while carboxyl group having -1 charge
Total charge = +1-1+0+1-1 = 0

At pH 9.9= Asp amino group having +0.5 charge while carboxyl having -1 charge
His side chain group posses 0 charge
Arg Side chain posses +1 charge while carboxyl group having -1 charge
Total charge = +0.5-1+0+1-1 = - 0.5
__________________
Kunal Pandya
Reply With Quote
Reply

Tags
asphisarg , calculate , charge , peptide , phs


Thread Tools
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are On
Pingbacks are On
Refbacks are On

Forum Jump

Similar Threads
Thread Thread Starter Forum Replies Last Post
Finding net charge on a peptide? Hermione Granger Peptide Forum 1 10-08-2012 03:44 AM
For a Tetrapeptide below HCYD Calculate the net charge of the peptide at pH = 6.00? Chuck Joe Peptide Forum 0 06-21-2011 08:54 AM
For a Tetrapeptide below HCYD Calculate the net charge of the peptide at pH = 6.00? Chuck Joe Peptide Forum 0 06-21-2011 08:54 AM
How to calculate the net charge of the peptide Arg-Phe-Gly-Lys-Glu at pH7? Jen Peptide Forum 0 07-10-2009 12:16 AM
Nobel Prize for David Thomson?! caltechdude Physics Forum 428 01-21-2005 10:39 PM


All times are GMT. The time now is 01:44 PM.


Powered by vBulletin® Version 3.8.4
Copyright ©2000 - 2014, Jelsoft Enterprises Ltd.
Copyright 2005 - 2012 Molecular Station | All Rights Reserved
Page generated in 0.12585 seconds with 16 queries