Net Charge of a a pentapeptide

[element41skater]

What isthe net charge of your pentapeptide at physiological pH 7.4 and pH 1.5?

 

 

This is my pentapeptide: ala-leu-glu-hos-his.

 

 

N-terminus has a pk~9

glu has a pk~4

his has a pk~6

c-terminus has a pk~3

 

 

How do i determine what the charges are for each amino acid, so that i can determine my net Charge?

 

 

 

 

Thank you

Alex

[Horza2002]

You know the pka of each of the functional groups present in the pentapeptide, so you know whether or not each group with be protonated or deprotonated. Once you know that, all you'll need to do is add up the total number of protonatied species and take away the deprotonated to leave you the overal charge.

[element41skater]

Why is the pH a concern then?

[Horza2002]

Because the pH will depend on whether the groups are protonated or deprotonated...

[element41skater]

What i am getting is

 

At pH 7.4:

N-terminus = +1

Glu= -1

his= -1

C-terminus= -1

net charge = -2

 

and

 

 

At pH 1.5:

 

N-terminus = +1

Glu= +1

his= +1

C-terminus= -1

net charge = +2

 

 

Not totally sure, i matched the pH and the pK values to determine if i had a positive or negative charge