Question

6. A peptide has the sequence Cys-His-Phe-Glu-Ala-Arg a. Write the single letter sequence of the peptide b. Calculate the percentage and indicate the charge of the predominant peptide species at pH 6.5. Use the following pKa values: pKa Cys = 8.3, pKa N-terminus = 10.8, pKa His =6.0, pKa Glu = 4.3, pKa Arg = 12.5, pKa C-terminus =2.0 c. What is the charge of the peptide at pH 4.3? d. Draw the chemical structure of the predominant peptide species at pH 9.0. Clearly indicate charged groups e. Calculate the pI of the peptide

Answer 1

@ A) Peptide seq- cys-His-Phe- Glu - Ala- Arg @ single letter sequence- C-H-F-E-A-R © charge at PH 6.5 =0 Explanation cys - Hin - phe - Glu-Ala - Ang prinin - PkRO PKR 8.3 6.0 4.3 12.5 Pk 101 10.8 PKR PKR * cys at aboue PH 8.80 Exixt as it as SH (below of co contain al change. Here at PH 6.5 Exipt as SH. * His side chain is weakly basic becomes neutraline at PH=6 and onwards. below PH=6 it has ti chage +1 -1 +1-1 = 0 © change at PH 4.3 = +2 + + +1 -1 = +2 Рk, M, A4 Рk,

D structure at PH=,9 11 09 H-C-N-CH-C-N-CH-C-N-CH-C | -I N | H CH-C-N-CH- | | | CH₂ 1 CH₂ CH2 " - CH₂ 2 ÇH2 ... CH₂ ... Coo", HN CH₂ CH NH Explanation - cys R group SH at PH 9 NHC 1? 2 1 NHA. Prose musent in s Jonim ni ..??.?.?? .? SHE'S +ht , files, ;:4. 1-8 Abone PMB !!!?

@ PI of peptida a PH at which Net channe of any aq or pestich becomes zero called inoelectric point or? I PK 2 - Gys-tip - phe - Glo - Alan Ayg-pk, ...PkR cys and His special case- below PH 6 meam from 1-6 Hip hane tl chage. cys PH l to 8 contain to change, PHg toll contain-1 chas so make sure how to come rew change at overall peptide At pH=7 +1=Pkz cys PKR = No change . . Ho change Glupka s SI 3 + 1 = -1 Se +1-1+1-1 - 0 TPI of peptich is = 7 :