ON THE BIOSYNTHESIS OF PSEUDOURIDINE AND OF PSEUDOURIDYLIC ACID IN AGROBACTERIUM TUMEFACIENS

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Abstract
Crude extracts prepared from the plant tumor inducing organism Agrobacterium tumefaciens were shown to convert uracil and D-ribose-5-phosphate to pseudouridine in stoichiometric amounts. The addition of the nucleotidase inhibitor sodium arsenate altered the course of the reactions involved in such a way that pseudouridylic acid became the product. Under these conditions, the latter was formed in the same relative concentrations as pseudouridine in experiments without inhibitor.The direct synthesis of pseudouridylic acid from the above precursors was found to be catalyzed by an enzyme which has been tentatively designated as "pseudouridylic acid synthetase". This enzyme was separated from the nucleotidase and purified 80-fold. Parameters such as pH optimum, required ion concentration, and Michaelis constants were determined.The data presented in this paper permit the first description of the biosynthetic pathway for pseudouridylic acid and for pseudouridine in a bacterium.