Given below are two statements, one is labelled as Assertion (A) and other one labelled as Reason (R).
Assertion (A) : The free histidine is a dominant buffering system at physiological pH than the protein-bound or dipeptide histidine.
Reason (R) : In proteins or dipeptides, the imidazole pKa decreases substantially-in combination with other amino acids- to a level which is more than 1 pH unit removed from intracellular pH.