Question

6 pts Let's consider a protein with two surface-exposed histidine residues. • Hisa is a “typical” histidine residue with pKa = 6.0 • His is involved in a stabilizing interaction (His-NH+ ... -0_C-Glu) with a neighboring glutamic acid residue. For Hisp, the Gibbs free energy of deprotonation at pH = 7.0 and T = 293 K is AG'° = +15 kJ mol-1. a) What is the fraction of protonated Hisa at pH = 7.0 and T = 293 K? b) What is the fraction of protonated Hisp at pH = 7.0 and T = 293 K? c) What is the pKa of Hisg at T = 293 K?

Answer 1

a). pka of Histidine reside = 6.0 formula for fraction of pratonated - Hya 7 pH = poka at lag CAJ Chat] where CAI is conceration of Base & CHA+J is concentration of Acid. fraction of protonated His a at pt = 2.0 7.0=6.0+ lay [ AJ CHAT] - = = 7.0- 6.0 - 1.0 las CA CHATI CAJ - CHATJ 100 = 10. fraction of Hat I + 10 = 0.09. 6 pka Hur. gibbs free energy first calculate pla interm of to soka = SG 2303RT is equale = +15 Kimat 2303 x 8.314 Jkt mal 293 where R= gasconstant = 8.314 J K imala - T=293k

[Pago No. (Date 1 ta = 15 X | 0 3 2 303 X 8.314 X 293 fraction fractonated of 7.0 = 2674 + Huso = lag CAJ Chaty las CAJ CHAT 7.0- 2674 = 4.326 CAJ - 104326 = 21, 183.61 Chat fraction of Hus = 1 14 211183.61 21, 184.61 0.0080472 = 4.72 x 10-5 @ folka of His at 293k. calculated in is 2.67% alove It is which part bl.