[Comparison of reactivities or uridine- and cytidine-2',3'-cyclophosphates as donors and uridine and cytidine as acceptors of phosphate under dinucleoside monophosphate synthesis catalyzed by RNAase A]. / Sravenenie reaktsionnoi sposobnosti uridini tsitidin-2',3'-tsiklofosfata kakdonorov, uridina i tsitidina kak aktseptorov fosfata v sinteze dinukleozidmonofosfatov, kataliziruemom RNKazoi A.

In order to determine the relative activity of pyrimidine nucleoside-2',3'-cyclophosphates as donors and nucleosides as acceptors of phosphate in the reaction of the internucleotide bond formation catalyzed by RNAase A (EC 3.4.1.22), a comparative synthesis of dinucleoside monophosphates UpU, UpC, CpU and CpC at three different enzyme concentrations (20, 40 and 70 mkg/ml) and two temperatures (0 degrees and -15 degrees) was carried out. The conversion rate of donor (U greater than p and C greater than p) during the synthesis and in the competitive reaction of hydrolysis strongly depends on the type of acceptor activity as compared to uridine. Based on the data of synthesis and simultaneous hydrolysis of U greater than p and C greater than p it may be concluded that in the both cases the latter donor is more reactive. The approaches to the determination of the substrate activity of the donors and acceptors for the evaluation of optimal conditions of the dinucleoside monophosphate synthesis depending on the donor--acceptor combination are discussed.

3-Ribosyl-6-methyluracil as a phosphate acceptor in the synthesis of the internucleotide bond catalyzed by pancreatic ribonuclease.

The synthesis of uridylyl-(3'-5')-3-ribosyl-6-methyluracil (UprmU) catalyzed by pancreatic ribonuclease (EC 3.4.1.22) has been performed using uridine 2', 3'-cyclic phosphate (U greater than p) as phosphate donor and 3-ribosyl-6-methyluracil (rmU) as phosphate acceptor. The rate of synthesis of UprmU is much higher than that of uridylyl-(3'-5')-uridine (UpU) in a control experiment under the same conditions with uridine as acceptor. The yields of UpU and UprmU were 20 and 17% respectively. The competitive hydrolysis of the initial U greater than p also proceeds faster when rmU is used as the acceptor. The relationship between the conformation of this nucleoside and its acceptor activity in the enzymatic synthesis of the internucleotide bond is discussed.

[Acceptor activity of 4-N-acetylcytidine in the synthesis of (3'-5')-internucleotide bond catalyzed by pancreatic nuclease]. / Aktseptornaia aktivnost' 4-N-atsetiltsitidina v sinteze (3'-5')-mezhnykleotidnoi sviazi, kataliziruemom pankreaticheskoi ribonukleazoi

Cytidine and 4-N-acetylcytidine were compared as phosphate acceptors in dinucleoside monophosphate synthesis catalyzed by pancreatic ribonuclease with uridine-2',3'-cyclophosphate and cytidine-2',3'-cyclo phosphate as phosphate donors. Because of low solubility of 4-N-acetylcytidine in water, the synthesis was carried out in aqueus-organic media. The results obtained indicate that acetylation of the exoaminogroup of cytidine decreases its acceptor activity. For the first time uridilyl-(3'-5')-4-N-acetylcytidine and cytidilyl-(3'-5')-4-N-acetylcytidine are prepared enzymatically by pancreatic ribonuclease.

[Effect of temperature and concentrations of initial components on synthesis of internucleotide bond catalyzed by pancreatic ribonuclease]. / Vliianie temperatury i kontsentratsil iskhodnykh komponentov na sintez mezhnukleotidnoi sviazi, kataliziruemi pankreaticheskoi ribonukeazoi

The synthesis of cytidylyu-(3,-5,)-cytidine (CpC) catalyzed by pancreatic ribonuclease at 23 degrees, 0 degrees, and -15 degrees C in Tris-HCl-buffer was compared with that in aqueous propan-2-0. The data obtained show that the increase in the yield of oligonucleotides in aqueous buffer at -15 degrees, observed earlier is rather a result of the concentration change in the reaction mixture caused by the freezing of water than by a temperature fall from 0 to -15 degrees. A 4-fold increase in the initial concentrations of the substrates and ribonuclease with respect to the concentrations used earlier leads to the yield of CC in a homogeneous solution at 0 degrees close to is yield found in the frozen mixture at -15 degrees.