Abstract

Tyrosine hydroxylase pterin cofactor has been isolated from bovine adrenal medulla tissue by means of column chromatography on Florisil and Dowex 50-H⁺ columns, and paper chromatography in several solvent systems. The cofactor has been identified as a 6-substituted, unconjugated pteridine by permanganate oxidation to pterin-6-carboxylic acid. Its paper chromatographic behavior and fluorescence spectrum are identical with those of biopterin. The concentration of this pterin in bovine adrenal medulla tissue is estimated to be approximately 10 nmoles/g of tissue. The low concentration of this cofactor in chromaffin tissue emphasizes its importance in the regulation of tyrosine hydroxylase activity and the potential susceptibility of the enzyme system to end product feedback inhibition by catecholamines, which, according to Nagatsu, Levitt, and Udenfriend [J. Biol. Chem. 239, 2910 (l964)], appear to antagonize the action of the cofactor competitively in this hydroxylation reaction.