BISC 330 Spring 2010 Lecture 5

BISC 330 Spring 2010 Lecture 5 - BISC330L:Biochemistry...

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BISC 330L:  Biochemistry Spring Semester 2010 USC Lecture:  Friday, 22 January 2010 1.Calculating pI… 1.More Chapter 2 material…
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pI:  Single amino acid; NO ionizable  R group  Isoelectric point can be calculated by    averaging the pK a  values for the  α carboxylic acid and  α -amino groups.   Example:  Glycine has a pI of about 6.   pI = [(2.35 + 9.78)/2] =  6.1    
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pI:  Single amino acid; WITH  ionizable  R group pK a  values:  2.1, 9.6, 10.8 At physiological pH, LYSINE has a net  positive charge (+1).  We have to increase the pH of the  solution to remove positive charge in  order to reach the pI.   The pI for lysine is simply the average  of the pK a s of the two -NH 3 +  groups.  pI = [(9.18 + 10.79)/2]  =  10.0       
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pI:  Single amino acid; WITH  ionizable  R group pK a  values:  2.1, 9.6, 4.1 It is safe to assume that at low pHs like  2.0 or 4.0, the  α -amino group will be  100% protonated and hold a charge of  +1 (it is at least 5 pH points away).  To balance this +1 charge, ONE -1  charge between the TWO groups with  lower pKa’s must be calculated.
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This note was uploaded on 08/30/2010 for the course BIO 320 taught by Professor Wu during the Spring '10 term at USC.

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BISC 330 Spring 2010 Lecture 5 - BISC330L:Biochemistry...

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