The peptide Special-K forms an alpha-helix that is broken at high temperatures.

Question

The peptide Special-K forms an alpha-helix that is broken at high temperatures. The fraction of peptide in the alpha-helical form (fraction = moles alpha-helical peptide/total moles of peptide), alpha H, was measured over a range of temperatures: Calculate the equilibrium constant, K, and molar Gibbs free energy, Delta G, for helix formation at 54.3 degree C (assume a 1M solution). What is the sign of Delta H (i.e., positive or negative) for the formation of the alpha-helix at this temperature? Provide a brief explanation for its sign. Special-K contains one histidine residue. Calculate the fraction of Special-K molecules in which the histidine is positively charged at 25 degree C and pH 6.5. You are given that: As the temperature of the peptide is increased, the Ka of the histidine residue will change. Based on this, will the fraction of charged histidine residues increase or decrease (you don't need to calculate a value, but show reasoning) as the temperature is raised from 25 degree C to 54.4 degree C at pH 7?

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