Phosphorylase specificity

For the alternative production of nucleosides, Zuffi and Monciardini have reported a process by a transglycosylation reaction catalyzed by uridine phosphor-ylase and purine nucleoside phosphorylase. Specifically, their invention generally relates to a process for immobilizing cells and to the use of a resin for immobilizing cells, and the process is exemplified by the production of 306 from l-p-o-arabino-furanosyluracil 315 and 314 (Scheme 12.82). Similar biotransformations for the preparation of 306 and 307 from 314 and arabinofuranosyluracil have been reported by Farina et al. (using Enterobacter aerogenes), and Hummel-Marquardt et al. (using esterases (e.g., pig liver esterase) or lipases). ... 

The review articles by Schramm (1998, 2003) provide a number of examples of the successful application of this protocol to the design of enzyme-specific transition state-like inhibitors. Among these, the transition state inhibitors of human purine nucleoside phosphorylase (PNP) are particularly interesting from a medicinal chemistry perspective, as examples of these compounds have entered human clinical trials for the treatment of T-cell cancers and autoimmune disorders. 

Meyerhof s discovery in yeast extracts of a phosphorylase (which he named hexokinaseP) led to more detailed investigations of the specificity of this enzyme. The enzyme, which has been crystallized,89 converts D-glucose,... 

Shames, and S. E. Ealick, Purine nucleoside phosphorylase. 3. Reversal of purine base specificity by site-directed mutagenesis, Biochemistry 36 11725 (1997). 

The enzyme has been found in Leuconostoc mesenteroides66 and Pseudomonas saccharophila.6 In a series of outstanding researches Doudoroff and Hassid with associates investigated the specificity requirements of sucrose phosphorylase from P. saccharophila. It was found that the enzyme exhibits an absolute specificity for the D-glucose moiety of its... 

P was incorporated into specific serine residues on the phosphorylase. Similar phosphorylation activated the liver enzyme (Sutherland et al., 1956). 

As is often the case, tissue-specific control mechanisms operate to optimise adaptation to particular conditions. For example, muscle contraction requires an increase in cytosolic calcium ion concentration (see Section 7.2.1, Figure 7.4). During exercise when energy generation needs to be increased, or from a more accurate metabolic point of view, when the ATP-to-ADP ratio falls rapidly, and the accompanying rise in [Ca2 + ] activate (i) glycogen phosphorylase which initates catabolism of... 

Glycogen phosphorylase isoenzymes have been isolated from liver, brain and skeletal muscle. All forms are subject to covalent control with conversion of the inactive forms (GP-b) to the active forms (GP-a) by phosphorylation on specific serine residues. This phosphorylation step, mediated by the enzyme phosphorylase kinase, is initiated by glucagon stimulation of the hepatocyte. Indeed, the same cAMP cascade which inhibits glycogen synthesis simultaneously stimulates glycogenolysis, giving us an excellent example of reciprocal control. 

This rational approach to drug design has been adopted in developing a specific inhibitor of the human cellular enzyme, purine nucleoside phosphorylase (PNP). PNP functions in the purine salvage pathway, catalysing the reversible reaction shown below ... 

Fluorescence and phosphorescence emission spectroscopy were employed to study the interaction of E. coli purine nucleoside phosphorylase (PNP) with its specific inhibitor, FA. The results show, for the first time, the application of phosphorescence spectroscopy to the identification of the tautomeric form of the inhibitor bound by the enzyme <2004MI377>. 

Idoxuridine (9.7) and trifluridine (9.8) are antiviral agents that are phosphorylated to their active form in virus-infected cells, and thus show specificity for two reasons their higher affinity for the viral enzyme, and the higher phosphorylase levels in viral-infected than in normal cells. Both compounds have been used locally on lesions of HSV-1 and HSV-2 (the latter of which causes genital herpes, now reaching epidemic proportions) with fair success. They are rather toxic if administered parenterally, as are all moderately selective antimetabolities. 

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