Acetyl-D-tyrosine

The tyrosine content of parenteral solutions is limited by poor tyrosine solubility. N-acetyl-L-tyrosine has excellent solubility and is a potential source of intravenous tyrosine. Infusion of N-acetyl-U-14C-L-tyrosine as part of a total parenteral nutrition regimen in the rat at a level of 0.5 mmol/kg/day resulted in rapid labeling of tissue tyrosine pools, production of 14CO2, incorporation of 14C-labeled tyrosine into protein, and modest urinary losses (8.3%). Plasma tyrosine levels, however, remained at fasting values (73.8 +/- 5.40 microM). Infusion of N-acetyl-L-tyrosine at 2 mmol/kg/day increased plasma tyrosine above fasting levels (141 +/- 16.1 microM), resulted in a rapid labeling of tissue tyrosine pools, production of 14CO2, and incorporation of 14C-labeled tyrosine into protein. However, urinary losses were higher (16.8%). Rapid utilization of N-acetyl-L-tyrosine was noted at both infusion levels. Plasma- and tissue-free tyrosine pools were rapidly labeled, as was tissue protein. Radioactivity incorporated in tissue protein was shown to be tyrosine after acid hydrolysis.

The title compound, C(11)H(11)Br(2)NO(4)·0.5H(2)O, was prepared by an electrophilic bromination of N-acetyl-l-tyrosine in acetonitrile at room temperature. The two independent mol-ecules do not differ substanti-ally and a mol-ecule of water completes the asymmetric unit. The synthesis of the title compound does not modify the stereochemical center, as shown by the absolute configuration found in this crystal structure. Comparison with the non-bromo starting material differs mainly by rotation features. For instance the H(methine)-C(chiral center)-C(methyl-ene)-C(ipso) is 173.0 (2)° torsion angle in one mol-ecule and 177.3 (2)° in the other, indicating a trans arrangement. This is in contrast with approximately 50° in the starting material. A short inter-molecular Br⋯Br separation is observed [3.2938 (3) Å]. The molecules in the crystal are connected via a network of hydrogen bonds through an N-H⋯O hydrogen bond between the hydroxy group of the phenol of the tyrosine and the N-H of the amide of the other molecule and an O-H⋯O hydrogen bond between the hydroxy group of the carboxylic acid and the oxygen of the carbonyl of the amide.

Under stress conditions, mitochondria release low levels of reactive oxygen species (ROS), which triggers a cytoprotective response, called "mitohormesis". It still remains unclear how mitochondria respond to stress-derived stimuli and release a low level of ROS. Here, we show that N-acetyl-l-tyrosine (NAT) functions as a plausible intrinsic factor responsible for these tasks in stressed animals. NAT is present in the blood or hemolymph of healthy animals, and its concentrations increase in response to heat stress. Pretreatment with NAT significantly increases the stress tolerance of tested insects and mice. Analyses using Drosophila larvae and cultured cells demonstrate that the hormetic effects are triggered by transient NAT-induced perturbation of mitochondria, which causes a small increase in ROS production and leads to sequential retrograde responses: NAT-dependent FoxO activation increases in the gene expression of antioxidant enzymes and Keap1. Moreover, we find that NAT represses tumor growth, possibly via the activation of Keap1. In sum, we propose that NAT is a vital endogenous molecule that could serve as a triggering factor for mitohormesis.