Carnosine in the context of histidine-containing dipeptides

Even though histidine constitutes one of the least abundant residues, it often plays key biochemical roles in protein environments due to the peculiar reactivity of the imidazole ring that characterizes its side chain. Such a relevant chemical profile can also explain the remarkable (and not yet fully clarified) biological roles played by histidine containing dipeptides and in particular by carnosine and its derivatives. Hence, the chapter starts by analyzing the key reactivity of the imidazole ring to explain and rationalize the biological properties of histidine-containing dipeptides as grouped into proteinogenic and nonproteinogenic compounds.