Hydrolysis of 2',3'-O-methyleneadenos-5'-yl bis(2',5'-di-O-methylurid-3'-yl) phosphate, a sugar O-alkylated trinucleoside 3',3',5'-monophosphate: implications for the mechanism of large ribozymes.
Hydrolytic reactions of 2',3'-O-methyleneadenos-5'-yl bis(2',5'-di-O-methylurid-3'-yl) phosphate (1), a sugar O-alkylated trinucleoside 3',3',5'-monophosphate, have been followed by RP HPLC over a wide pH range. Under neutral and mildly acidic conditions, the only reaction observed was a pH-independent cleavage of the O-C5' bond of the 5'-linked nucleoside. Under more alkaline conditions nucleophilic attack by hydroxide ion starts to compete. The reaction is first order in [OH(-)] and becomes predominant at pH 10. Each of the 3'-linked nucleosides is displaced 2.9 times as readily as the 5'-linked one. To determine the beta(lg) value for the hydroxide ion catalyzed hydrolysis of 1, two diesters (2a,b) having 2',3'-O-methyleneadenosine (7) and 2',5'-di-O-methyluridine (4) as leaving groups were hydrolyzed under alkaline conditions. Since the beta(lg) value for this reaction is known, DeltapK(a) between 4 and 7 could be calculated. The beta(lg) for the hydrolysis of 1 was estimated to be -0.5 with use of this information. The mechanisms of the partial reactions and the role of leaving group properties in ribozyme reactions of large ribozymes are discussed.
Lönnberg
Tuomas
T
Department of Chemistry, University of Turku, Vatselankatu 2, FIN-20014 Turku, Finland. tuanlo@utu.fi
Mikkola
Satu
S
D000241:Adenosine / Q000031:analogs & derivatives*; D002851:Chromatography, High Pressure Liquid / Q000379:methods; D006863:Hydrogen-Ion Concentration; D006868:Hydrolysis; D007700:Kinetics; D010756:Phosphoric Acids / Q000737:chemistry*; D016337:RNA, Catalytic / Q000737:chemistry* / Q000378:metabolism; D014529:Uridine / Q000031:analogs & derivatives*
D010756:Phosphoric Acids; D016337:RNA, Catalytic; D000241:Adenosine; D014529:Uridine