n-acetyl-l-histidine monohydrate

N-Acetyl-L-histidine monohydrate (NAH) is a histidine derivative and a prominent biomolecule found in the brain, retina, and lens of poikilothermic (cold-blooded) vertebrates. It functions as an essential animal metabolite and serves as a major osmolyte in the brain and ocular tissues of teleost fish, amphibians, and reptiles. Unlike poikilotherms, homeothermic (endothermic) vertebrates exhibit significantly lower levels of NAH in the brain and other tissues, highlighting its unique phylogenetic distribution and specialized physiological role in evolutionary biology and vertebrate homeostasis.