L-URIDINE: SYNTHESIS AND BEHAVIOR AS ENZYME SUBSTRATE^*

Abstract

L-Uridine, the enantiomer of the normal RNA constituent D-uridine, was synthesized from L-ribose through coupling with bis(trimethylsilyl)-uracil. The synthetic product had the expected chemical and physical characteristics. When used as the acceptor for phosphate transfer by the nucleoside phosphotransferase of carrot, L-uridine is converted to 5′-L-uridylic acid. The Michaelis constants K_m are 28 × 10^-3 M for L-uridine, 5 × 10^-3 M for D-uridine. The nucleoside phosphotransferase of human prostate, which phosphorylates D-uridine in the 5′, 3′, or 2′ positions, fails to transfer phosphate to the 2′ position of L-uridine, but does produce 5′-and 3′-L-uridylic acids.