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Step 1: Determine the total positive charge on the hexapeptide when all acidic and basic groups are fully protonated. Enter your answer without the sign. charge: Step 2: Determine the pK value of the group that loses a proton to form the zwitterionic species with a net charge pK = of zero. Step 3: Determine the pK value of the group that gains a proton to form the zwitterionic species with a net charge pK = of zero. Step 4: Estimate the pl value of the hexapeptide. pI =

Step 1: Determine the total positive charge on the hexapeptide when all acidic and basic groups are fully protonated. Enter your answer without the sign. charge: Step 2: Determine the pK value of the group that loses a proton to form the zwitterionic species with a net charge pK = of zero. Step 3: Determine the pK value of the group that gains a proton to form the zwitterionic species with a net charge pK = of zero. Step 4: Estimate the pl value of the hexapeptide. pI =

Chemistry
Chemistry
10th Edition
ISBN:9781305957404
Author:Steven S. Zumdahl, Susan A. Zumdahl, Donald J. DeCoste
Publisher:Steven S. Zumdahl, Susan A. Zumdahl, Donald J. DeCoste
Chapter1: Chemical Foundations
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Problem 1RQ: Define and explain the differences between the following terms. a. law and theory b. theory and...
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### Hexapeptide Charge and pK Analysis **Step 1**: Determine the total positive charge on the hexapeptide when all acidic and basic groups are fully protonated. Enter your answer without the sign. - **Charge**: [ _______ ] **Step 2**: Determine the pK value of the group that **loses** a proton to form the zwitterionic species with a net charge of zero. - **pK**: [ _______ ] **Step 3**: Determine the pK value of the group that **gains** a proton to form the zwitterionic species with a net charge of zero. - **pK**: [ _______ ] **Step 4**: Estimate the pI value of the hexapeptide. - **pI**: [ _______ ]
Transcribed Image Text:### Hexapeptide Charge and pK Analysis **Step 1**: Determine the total positive charge on the hexapeptide when all acidic and basic groups are fully protonated. Enter your answer without the sign. - **Charge**: [ _______ ] **Step 2**: Determine the pK value of the group that **loses** a proton to form the zwitterionic species with a net charge of zero. - **pK**: [ _______ ] **Step 3**: Determine the pK value of the group that **gains** a proton to form the zwitterionic species with a net charge of zero. - **pK**: [ _______ ] **Step 4**: Estimate the pI value of the hexapeptide. - **pI**: [ _______ ]
### Understanding Isoelectric Focusing and pI Calculation of Peptides Isoelectric focusing can separate peptides based on their relative contents of acidic and basic residues. When voltage is applied to an electrophoretic gel with a pH gradient, each peptide migrates until it reaches a point where it has no net charge. This pH at this point is referred to as the isoelectric point (pI) for the peptide. One can estimate the pI fairly accurately (within 0.1 or 0.2 pH units) using the pK values of all the proton dissociable groups in the peptide. #### Example Hexapeptide Consider the hexapeptide **Met-Asp-Lys-Arg-Ala-Tyr**. #### Reference Table of pK Values | Amino acid | pK | | ------------------ | ---- | | Arg | 12.5 | | Asp | 3.7 | | Cys | 8.2 | | Glu | 4.3 | | His | 6.0 | | Lys | 10.5 | | Tyr | 10.5 | | *peptide-NH₃⁺ | 8.0 | | *peptide-COOH | 3.4 | **Note:** Amino and carboxyl terminal values differ from the α amino and carboxy values of a single amino acid. ### Calculating the Total Positive Charge **Step 1:** Determine the total positive charge on the hexapeptide when all acidic and basic groups are fully protonated. Enter your answer without the sign. **Charge:** [Input Box] ### Detailed Explanation of the Table The table provided lists the pK values for the amino acids and terminal groups. Each amino acid has specific pK values that need to be considered for calculating the net charge at a given pH, and ultimately the pI of the peptide. For instance: - **Arg** has a high pK value of 12.5, indicating it will contribute to the positive charge until the pH exceeds this value. - **Asp** and **Glu** have low pK values (3.7 and 4.3, respectively) indicating they will lose their proton and contribute to the negative charge at relatively low pH values. Using this table, you can sequentially determine which groups
Transcribed Image Text:### Understanding Isoelectric Focusing and pI Calculation of Peptides Isoelectric focusing can separate peptides based on their relative contents of acidic and basic residues. When voltage is applied to an electrophoretic gel with a pH gradient, each peptide migrates until it reaches a point where it has no net charge. This pH at this point is referred to as the isoelectric point (pI) for the peptide. One can estimate the pI fairly accurately (within 0.1 or 0.2 pH units) using the pK values of all the proton dissociable groups in the peptide. #### Example Hexapeptide Consider the hexapeptide **Met-Asp-Lys-Arg-Ala-Tyr**. #### Reference Table of pK Values | Amino acid | pK | | ------------------ | ---- | | Arg | 12.5 | | Asp | 3.7 | | Cys | 8.2 | | Glu | 4.3 | | His | 6.0 | | Lys | 10.5 | | Tyr | 10.5 | | *peptide-NH₃⁺ | 8.0 | | *peptide-COOH | 3.4 | **Note:** Amino and carboxyl terminal values differ from the α amino and carboxy values of a single amino acid. ### Calculating the Total Positive Charge **Step 1:** Determine the total positive charge on the hexapeptide when all acidic and basic groups are fully protonated. Enter your answer without the sign. **Charge:** [Input Box] ### Detailed Explanation of the Table The table provided lists the pK values for the amino acids and terminal groups. Each amino acid has specific pK values that need to be considered for calculating the net charge at a given pH, and ultimately the pI of the peptide. For instance: - **Arg** has a high pK value of 12.5, indicating it will contribute to the positive charge until the pH exceeds this value. - **Asp** and **Glu** have low pK values (3.7 and 4.3, respectively) indicating they will lose their proton and contribute to the negative charge at relatively low pH values. Using this table, you can sequentially determine which groups
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