L-Histidine Monohydrochloride Monohydrate, 25g

The essential amino acid L-histidine is one of the three amino acids with a basic side chain, and is very hydrophilic in character. It contains an imidazole group in the side chain. L-Histidine has been used to study cultures of the human T-lymphoblastic leukemia cell line MOLT-4 to study modulation of apoptosis. Exogenous histidine has been shown to enhance the biosynthesis of lovastatin by cultured Aspergillus terreus. Histidine has been utilized as a single nitrogen source to probe swarming in Pseudomonas aeruginosa on agar. An in vivo study has used L-histidine to diminish the net secretory response of the small intestine of of cholera toxin-challenged mice. Because the pKa of the imidazole group is close to physiological pH, the imidazole moiety can be either uncharged or positively charged, depending on the local environment. This property makes histidine residues of exceptional interest in the active sites of many proteins, such as hemoglobin and myoglobin, where the imidazole ring can readily alternate between the charged (imidazolium) and uncharged (imidazole) states to participate in bond formation and breakage. Histidine is biosynthesized from ATP, 5-phosphoribosyl-1-pyrophosphate (PRPP), and glutamine. In turn, histidine is degraded to glutamate by histidase, urocanase, and imidazolonepropionase via the formation of urocanate, 4-imidazolone 5-propionate, and N-formiminoglutamate.