| Abstract: | The stereochemical problem involving a pro-pro-prochiral phosphorus center, the hydrolysis of adenosine 5'-monophosphate to adenosine and inorganic phosphate catalyzed by the venom 5'-nucleotidase, has been studied by use of chiral 16O, 17O, 18O]thiophosphates (Psi). (Rp)- and (Sp)-alpha-18O1]Adenosine 5'-thiophosphates (AMPS) were synthesized by a combined chemical and biochemical procedure. Hydrolysis of (Rp)- and (Sp)-alpha-18O1]AMPS in H217O by 5'-nucleotidase gave two enantiomers of chiral Psi of unknown configuration. A 31P NMR method based on the combination of the quadrupolar effect of 17O Tsai, M.-D. (1979) Biochemistry 18, 1468-1472] and the 18O isotope shift Cohn, M., & Hu. A. (1978) Proc. Natl. Acad. Sci. U.S.A. 75, 200-203] has been developed to analyze the configuration of chiral Pso. The results indicate that hydrolysis of (Rp)- and (Sp)-alpha-18O1]AMPS in H217O gave (R)- and (S)- 16O, 17O, 18O]Psi, respectively. Therefore the hydrolysis of AMPS catalyze by the venom 5'-nucleotidase must proceed with inversion of configuration at phosphorus, which suggests that the reaction is most likely an "in line" single displacement without involving a phosphoryl-enzyme intermediate and without pseudorotation. |
