| Abstract: | Nucleoside phosphotransferase from barley seedlings was used to catalyze the equilibration of adenosine-5'-18O]phosphorothioate having the S configuration at phosphorus with adenine-8-14C]adenosine to produce adenine-8-14C]adenosine-5'-18O]phosphorothioate and adenosine. The configuration of the chiral phosphorus in adenosine-5'-18O]phosphorothioate which was used as the donor substrate was then compared with that of the adenine-8-14C]adenosine-5'-18O]phosphorothioate isolated from the reaction mixture. They were found to be the same, showing that the reaction proceeds with 99.7% retention of configuration of the 18O]phosphorothioate. This is interpreted to be indicative of the involvement of a thiophosphoryl-enzyme intermediate in the nucleoside phosphotransferase reaction. The synthesis of adenosine-5'-18O]phosphorothioate having the R and S configurations at the phosphorus atoms is described. |
