V-M-Y-F-E-N: This is the single-letter amino acid...

V-M-Y-F-E-N: This is the single-letter amino acid abbreviation for a peptide. What is the net charge of this peptide at $\mathrm{pH} 7.0 ?$ An enzyme called a protein tyrosine kinase can attach phosphates to the hydroxyl groups of tyrosine. What is the net charge of the peptide at $\mathrm{pH} 7.0$ after it has been phosphorylated by a tyrosine kinase? What is the likely source of phosphate utilized by the kinase for this reaction?

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Key Concepts

Peptide Ionization at Physiological pH

This concept involves understanding how the ionizable groups of a peptide—namely, the amino terminus, carboxyl terminus, and ionizable side chains—acquire or lose protons based on the pH of the solution. At physiological pH (around 7.0), these groups have characteristic pKa values that determine their protonation state, ultimately affecting the peptide's net charge.

Phosphorylation and Charge Modulation

Phosphorylation is a post-translational modification where a phosphate group is covalently attached to specific amino acid residues, such as tyrosine. This modification introduces additional negative charges (due to the deprotonated phosphate at neutral pH) to the molecule, thereby altering the overall charge and potentially influencing the protein’s function and interactions.

ATP as a Phosphate Donor in Kinase Reactions

ATP (adenosine triphosphate) serves as the primary phosphate donor in kinase-mediated phosphorylation reactions. In these reactions, protein kinases transfer the terminal phosphate group from ATP to a target amino acid residue on a protein or peptide, converting ATP into ADP. This process is fundamental in regulating various cellular signaling pathways.

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