2.2 pt Below is the sequence of a small protein shown in single-letter abbreviat

Question

2.2 pt Below is the sequence of a small protein shown in single-letter abbreviations (sve ig 3 2 or Handout D) from the Tobacco Hornworm gut for this insect is very alkaline (pH 10.5), and that is the optimal pH for this protein (maximum enzyme activity). Label the charge (+",""N" for neutral) above each amino acid along the full length of this protein while at its optimal pH. Then, calculate the overal charge ("net charge") for this protein when present in the Manduca mid-gut. (Manduca sexta) insect mid-gut. The pH of the mid- N-terminus: M-A-D-K-Y-K-F-W-P-Y-H-R-C-Y-S-D-R-G :C-terminus 20 2 3 4 6 tab

Explanation / Answer

Answer:

The given sequence of protein is:

Single letter code:

NH2- MADKYKFWPYHRCYSDRG -COOH

Triple letter code:

NH2- Met - Ala - Asp - Lys - Tyr - Lys - Phe - Trp - Pro - Tyr - His - Arg - Cys - Tyr - Ser - Asp - Arg - Gly -COOH

Number of residues: 18

Expected net charge on amino acids pI values for different amino acids is as shown in table below:

So expected net charge on protein at pH 10.5 = -3

pKa (R - residue) Net Charge at pH 7 Met Neutral Ala Neutral Asp 3.65 - Lys 10.79 + Tyr 10.46 0 Lys 10.79 - Phe Neutral Trp Neutral Pro Neutral Tyr 10.46 0 His 6 - Arg 12.48 + Cys 8.33 - Tyr 10.46 0 Ser Neutral Asp 3.65 - Arg 12.48 + Gly Neutral Carboxy terminus 2 - Amino terminus 0 Net Charge =-6+3 = -3

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