C₁₉H₂₇N₇O₂₁P₄; MW 813.4 (free acid); λ_max 260 nm; ε 25000; sodium salt, purity > 95% HPLC. Synonym: P¹- (5’- Adenosyl)- P⁴- (5’- uridyl)- tetraphosphate. Up₄A is a dinucleoside polyphosphate containing both, a purine as well as a pyrimidine nucleobase moiety. It is considered to be a novel endothelium-derived vasoconstrictive factor. Detailed technical information and references available. Reference: Jankowski et al., Nature Medicine, 11, 223 - 227 (2005).