Kinetics and Mechanism of Facile and Selective Dephosphorylation of 2'-Phosphorylated and 2'-Thiophosphorylated Dinucleotides: Neighboring 3'-5' Phosphodiester Promotes 2'-Dephosphorylation.
2'-Phosphorylated and 2'-thiophosphorylated dinucleotides U(2'-p)pU (1) and U(2'-ps)pU (2) were found to undergo facile 2'-specific dephosphorylation at 90 degrees C in neutral aqueous solution to give UpU, and the first-order rate constants of these reactions were determined by HPLC. Particularly, U(2'-ps)pU (2, k = 1.38 +/- 0.4 x 10(-)(3) s(-)(1), t(comp) = 1 h) was cleanly dephosphorylated ca. 100 times more rapidly than U(2'-p)pU (1, k = 1.41 +/- 0.05 x 10(-)(5) s(-)(1), t(comp) = 72 h). Dephosphorylations of 1 and 2 were faster than those of thymidine 3'-phosphate (8) and thymidine 3'-thiophosphate (9), respectively. The kinetic data observed were independent of the 2'- or 3'-position of the phosphate group and the kind of base moiety. The neighboring 3'-5' phosphodiester function most probably promotes the 2'-dephosphorylation efficiently. A branched trimer, U(2'-pU)pU (3), and related compounds having a substituent on the 2'-phosphoryl group, such as U(2'-pp-biotin)pU (4) and U(2'-ps-bimane)pU (5), were rather resistant to hydrolysis. The addition of divalent metal ions (Mg(2+), Mn(2+), Zn(2+), Ca(2+), Co(2+), and Cd(2+)) remarkably decreased the rate of 2'-de(thio)phosphorylation of 1 or 2. Among these metal ions, Zn(2+) most significantly inhibited the dephosphorylation. On the contrary, trivalent metal ions considerably accelerated the 2'-de(thio)phosphorylation of 1 or 2. The mechanism of 2'-dephosphorylation in the presence and absence of various metal ions is also discussed.
Tsuruoka
Hiroyuki
H
Department of Life Science, Tokyo Institute of Technology, Nagatsuta, Midoriku, Yokohama 226, Japan.
Shohda Ki
Koh-ichiroh
Wada
Takeshi
T
Sekine
Mitsuo
M