Examine the following peptide Thr Glu pro xle Val Ala P

Examine the following peptide Thr- Glu - pro - xle - Val - Ala - Pro - Mel - Glu - Tyr - Gly - Lys What will be the net charge @ pH 7 @ pH 12 @ pH 4. Which side is the amino terminal and which side is carboxy terminal

Solution

At PH4 the charge on the peptide will be 0

Because at this PH the both Glu COOH group will be in deprotonated COO^- form and the N-terminal and lysine NH₃ will be in protonated form so the net charge will be 0.

At PH 7

The net charge will be -1

because the N-terminal NH₃ will be in deprotonated form and and Lysine NH₃ will be in protobated form and both COOH group of glutamate will be in deprotonated form so net charge will be -1.

At PH 12 the net charge will be -4

because all NH_3⁺ will be in deprotonated form (NH₃₎ and all 4 COOH group will also in deprotonated form COO^- so net charge will be 4.

The Amino and Corboxy terminal of the peptide

NH2- Thr - Glu - Pro - Ile - Val - Ala - Pro - Met - Glu - Tyr - Gly - Lys -COOH