Cyril S. Alexeev

Substrate specificity of Escherichia coli thymidine phosphorylase

Substrate specificity of Escherichia coli thymidine phosphorylase to thymidine derivatives modified at 5′-, 3′-, and 2′,3′-positions of the sugar moiety was studied. Equilibrium and kinetic constants (Km, KI, kcat) of the phosphorolysis reaction have been determined for 20 thymidine analogs. The results are compared with X-ray and molecular dynamics data. The most important hydrogen bonds in the enzyme-substrate complex are revealed.

Substrate Specificity of Thymidine Phosphorylase of E. Coli: Role of Hydroxyl Groups

Substrate specificity of E. coli thymidine phosphorylase to pyrimidine nucleoside modified at 5 ′-, 3 ′-, and 2 ′-positions of sugar moiety has been studied. Equilibrium (Keq) and kinetics constants of phosphorolysis reaction of nucleosides were measured. The most important hydrogen bonds in enzyme-substrate complex have been determined.

Synthesis of Cytokinins via Enzymatic Arsenolysis of Purine Nucleosides

This unit describes an effective method for the preparation of natural cytokinins and their synthetic derivatives based on enzymatic cleavage of the N‐glycosidic bond of N6‐substituted adenosine or O6‐substituted inosine derivatives in the presence of purine nucleoside phosphorylase (PNP) and Na2HAsO4. The arsenolysis reaction is irreversible due to the hydrolysis of the resulting α‐D‐ribose‐1‐arsenate. As a result, the desired products are formed in near‐quantitative yields, as indicated by high‐performance liquid chromatography (HPLC) analysis, and can easily be isolated. In the strategy used here, the ribose residue acts as a protective group.

Substrate specificity of E. coli uridine phosphorylase. Further evidences of high-syn conformation of the substrate in uridine phosphorolysis

ABSTRACT Twenty five uridine analogues have been tested and compared with uridine with respect to their potency to bind to E. coli uridine phosphorylase. The kinetic constants of the phosphorolysis reaction of uridine derivatives modified at 2′-, 3′- and 5′-positions of the sugar moiety and 2-, 4-, 5- and 6-positions of the heterocyclic base were determined. The absence of the 2′- or 5′-hydroxyl group is not crucial for the successful binding and phosphorolysis. On the other hand, the absence of both the 2′- and 5′-hydroxyl groups leads to the loss of substrate binding to the enzyme. The same effect was observed when the 3′-hydroxyl group is absent, thus underlining the key role of this group. Our data shed some light on the mechanism of ribo- and 2′-deoxyribonucleoside discrimination by E. coli uridine phosphorylase and E. coli thymidine phosphorylase. A comparison of the kinetic results obtained in the present study with the available X-ray structures and analysis of hydrogen bonding in the enzyme-substrate complex demonstrates that uridine adopts an unusual high-syn conformation in the active site of uridine phosphorylase.