A titration curve of histidine illustrates how its pH changes as the volume of a titrant, like sodium hydroxide, increases. Histidine displays several points of equivalence in this curve. This display occurs because histidine, just like any other polyprotic acid, has incomplete dissociation.
Histidine is one of the simplest amino acids found in many of the known proteins. The amino acid is of great nutritional value, especially in vertebrates. It is also a source of an amine that is responsible for the contraction of smooth muscles and dilation of capillaries. It is also involved in the process of secreting gastric acid.