BISC 330 Spring 2010 Lecture 5

BISC 330 Spring 2010 Lecture 5 - BISC 330L: 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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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. Take the average :
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This note was uploaded on 01/30/2010 for the course BISC 330 taught by Professor Petruska during the Spring '08 term at USC.

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

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