L-uridine: synthesis and behavior as enzyme substrate.

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 x 10(-3)M for L-uridine, 5 x 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.